Seems like APNS is enforced since JM for iOS Version 14.1.2.
Up until that Jabber version IM/calling still worked with the legacy VoIP sockets (read Jabber Mobile still worked even if APNS wasn't turned on).
See Solved: Jabber iOS unregistered within a minute - Cisco Community
APNS is unsuited for restricted networks and poses a major challenge for such setups. (Finance, military, cruise ships, police, oil rigs, healthcare - you get the idea)
Apple has introduced local push connectivity for those specific use cases, it's currently not implemented in CUCM though. I see some NDA Cisco Live sessions scheduled for June 13th here -> Re: [UPDATE] Cisco Live 2022 Exclusive Roadmap Sessions - Page 3 - Cisco Community where they shed some light on the future CUCM roadmap. Might be the right place to ask about the local push connectivity feature or get the latest official news about what's on their backlog.