Hi Sylvain Leroux, Some time ago I also asked this question here. I think no one knows how to do it without rfcomm util.I use dbus-send for read dbus properties and now work non-interactive mode bluetoothctl.
I tried something like that: ---- busctl call \ org.bluez /org/bluez org.bluez.ProfileManager1 RegisterProfile \ 'osa{sv}' \ /bluez \ "00001101-0000-1000-8000-00805f9b34fb" \ 3 'Role' s server 'Channel' u 1 Name s 'SerialPort' ----
----------- Best regards, Aleksandr Proklov