apparmor is partially supported (check nixos security. apparmor, some manual configuration may be needed), not selinux though and probably never will be
sms is essentialy just a confirmation code delivery protocol tho? (like i have around 100 "chats" with just confirmation codes in them and ZERO conversations...) and i don't see anyone using rcs mostly because of EXTREMELY poor reputation of sms messaging...
or you can allow public authenticated access to dns over https... (just don't expose the raw udp dns server, it's a really bad idea)
(not sure if DoT can also support auth, but if it does that's great because android supports dot natively)
the clock app has a built in spotify integration and player.
the calculator sends diagnostic data.