The TestDisconnect test doesn't work for Interbase because the test is written for Firebird only. It seems that Interbase provides similar tables to Firebird and by updating these tables it seems to be possible to disconnect the connections there too:
https://docwiki.embarcadero.com/InterBase/2020/en/TMP$ATTACHMENTS
https://docwiki.embarcadero.com/InterBase/2020/en/Updating_System_Temporary_Tables
So if the test can be adapted, we maybe could make it pass on Interbase too.