I cannot reproduce your issue.
To enable XDMCP, I think you enable GDM login screen at console and a process of ibus-daemon is running owned by gdm user.
Xephyr process shows GDM login screen remotely and it runs another ibus-daemon is running owned by gdm user.
Both the GDM login screen and ibus-daemon is terminated with the timeout.
If I log into the GNOME session via GDM login screen, ibus-daemon runs owned by the session user but the both the session and ibus-daemon is terminated with the timeout.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (ibus bug fix update), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2023:4822