I'm sorry again for a stupid question about not running vdagentd, -- make install is our friend, heh :) Now all is ok with it.
I've also built spice-vdagentd with systemd-logind support now.
So, after make install and VM reboot we have login screen with mouse, and trying to log in... Login screen is fine but after login no mouse at all.
Here goes the log of vdagentd. I run spice-vdagentd.service with '-dd' as extra parameters.
[root@localhost ~]# journalctl -f -u spice-vdagentd.service
-- Logs begin at Thu 2021-08-26 23:20:26 MSK. --
авг 26 23:20:36 localhost.localdomain spice-vdagentd[2123]: New session agent does not belong to user: disabling file-xfer
авг 26 23:20:36 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de4e0 sent file xfer disable, arg1: 0, arg2: 0, size 0
авг 26 23:20:37 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de4e0 received guest xorg resolution, arg1: 2560, arg2: 1600, size 20
авг 26 23:20:37 localhost.localdomain spice-vdagentd[2123]: updating uinput size to 2560x1600, screen positions:
авг 26 23:20:37 localhost.localdomain spice-vdagentd[2123]: screen 0: +0+0
авг 26 23:20:37 localhost.localdomain spice-vdagentd[2123]: opening vdagent virtio channel
авг 26 23:20:37 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_3c1'
авг 26 23:20:57 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_3c1'
авг 26 23:20:57 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_3c1'
авг 26 23:20:57 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_3c1'
авг 26 23:21:26 localhost.localdomain spice-vdagentd[2123]: New client connected
авг 26 23:21:26 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de4e0 sent graphics device info, arg1: 0, arg2: 0, size 39
авг 26 23:21:26 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de4e0 received guest xorg resolution, arg1: 2560, arg2: 1600, size 20
авг 26 23:21:26 localhost.localdomain spice-vdagentd[2123]: updating uinput size to 2560x1600, screen positions:
авг 26 23:21:26 localhost.localdomain spice-vdagentd[2123]: screen 0: +0+0
авг 26 23:21:26 localhost.localdomain spice-vdagentd[2123]: Set max clipboard: 104857600
авг 26 23:21:26 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de4e0 sent audio volume sync, arg1: 0, arg2: 0, size 7
авг 26 23:21:29 localhost.localdomain spice-vdagentd[2123]: mouse-event: mon 0 916x407
авг 26 23:21:29 localhost.localdomain spice-vdagentd[2123]: mouse: abs-x 916
авг 26 23:21:29 localhost.localdomain spice-vdagentd[2123]: mouse: abs-y 407
авг 26 23:21:29 localhost.localdomain spice-vdagentd[2123]: mouse: syn
... mouse movement skipped ...
авг 26 23:21:45 localhost.localdomain spice-vdagentd[2123]: mouse-event: mon 0 1173x797
авг 26 23:21:45 localhost.localdomain spice-vdagentd[2123]: mouse: btn-left up
авг 26 23:21:45 localhost.localdomain spice-vdagentd[2123]: mouse: syn
...and somewhere about here user is logged in and mouse is completely disappeared along with reactions to mouse keypresses...
авг 26 23:21:50 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_3c1'
авг 26 23:21:50 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_3c1'
авг 26 23:21:50 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_3c1'
авг 26 23:21:50 localhost.localdomain spice-vdagentd[2123]: Active session: 4
авг 26 23:21:50 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:50 localhost.localdomain spice-vdagentd[2123]: (nil) is now the active session
авг 26 23:21:50 localhost.localdomain spice-vdagentd[2123]: closed vdagent virtio channel
авг 26 23:21:50 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:50 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:50 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:51 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:51 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:51 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:51 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: new client accepted: 0x55bcda5de660
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: Session for pid 2976: 4
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 sent version, arg1: 0, arg2: 0, size 7
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 is now the active session
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: (systemd-login) class for 4 is user
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 sent graphics device info, arg1: 0, arg2: 0, size 39
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 received guest xorg resolution, arg1: 2560, arg2: 1600, size 20
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: updating uinput size to 2560x1600, screen positions:
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: screen 0: +0+0
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: opening vdagent virtio channel
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 sent graphics device info, arg1: 0, arg2: 0, size 39
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 sent graphics device info, arg1: 0, arg2: 0, size 39
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 sent client disconnected, arg1: 0, arg2: 0, size 0
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de4e0 sent client disconnected, arg1: 0, arg2: 0, size 0
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: New client connected
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: Set max clipboard: 104857600
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: No QXL devices found, not generating xorg.conf
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 sent monitors config, arg1: 0, arg2: 0, size 328
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 sent graphics device info, arg1: 0, arg2: 0, size 39
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 sent audio volume sync, arg1: 0, arg2: 0, size 7
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 sent audio volume sync, arg1: 0, arg2: 0, size 7
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: Set max clipboard: 104857600
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: No QXL devices found, not generating xorg.conf
авг 26 23:21:55 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 sent monitors config, arg1: 0, arg2: 0, size 328
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 received guest xorg resolution, arg1: 2560, arg2: 1600, size 20
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: updating uinput size to 2560x1600, screen positions:
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: screen 0: +0+0
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 received guest xorg resolution, arg1: 2560, arg2: 1600, size 20
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: updating uinput size to 2560x1600, screen positions:
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: screen 0: +0+0
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 received guest xorg resolution, arg1: 2560, arg2: 1600, size 20
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: updating uinput size to 2560x1600, screen positions:
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: screen 0: +0+0
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: Error receiving data: Connection reset by peer
авг 26 23:21:56 localhost.localdomain spice-vdagentd[2123]: (nil) is now the active session
авг 26 23:21:57 localhost.localdomain spice-vdagentd[2123]: closed vdagent virtio channel
авг 26 23:21:57 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de660 disconnected
авг 26 23:22:02 localhost.localdomain spice-vdagentd[2123]: 0x55bcda5de4e0 disconnected
авг 26 23:22:02 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:22:02 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:22:02 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:22:02 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:22:02 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:22:02 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
авг 26 23:22:02 localhost.localdomain spice-vdagentd[2123]: logind match: type='signal',interface='org.freedesktop.login1.Session',path='/org/freedesktop/login1/session/_34'
... and reconnect nor connect via QEMU VNC can resurrect mouse here...