PG 14.10 and 15.5, if it matters.
Running pg_terminate_backend() on the walsender pid (and then dropping the replication slot) seems the canonical solution, based on StackExchange, but that leaves primary_conninfo in postgresql.auto.conf and standby.signal in $PGDATA.
Promoting the secondary (and then dropping the replication slot) handles all those issues, but leaves it in R/W mode, which might cause split brain issues with cluster managers.
Is there a better way than the two I've described