

Sorry, I just saw the recommendations. I’m using a Matrix server myself. And it’s connected to the internet, since I use it 24/7 and on my phone, etc.
I guess technically, most protocols can be used in an internal network. But maybe you’ll need to put in some extra effort, for example if a platform requires SSL certificates or something like that.
I mean you could try… If it asks for a hostname, just put a local hostname in. Or the IP address. Or set up a DNS entry on the router. And see if it works.
Or try something like RocketChat, or depending how your team’s workflow is, maybe you don’t want a messenger. But some (online) collaboration platform more focused on documents, like Nextcloud.

I feel the majority of it isn’t really Android, but some Google Apps… Google Camera, Instagram, Find hub… RCS messages aren’t in AOSP either… The threat detection will be inside of the Google services… So I won’t get most of this on my phone. And I wonder if OS verification and hardware isolation are features to protect my security, or whether that’s to safeguard some DRM stuff and whatever some dubious app developers don’t want me to touch on my own phone.