This is by far one of the most commonly asked questions lately. Have you spent any time searching for the topic on either the community or with a regular search on internet. What you should be looking at is APNS, short for Apple Push Notification Services.
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.