According to signal facts all the have is your phone number and and the date you signed up for the service and the last day you connected to the server. IP address are not logged or stored the do t have access to it and signal has said this everytime the get a warrent for user data. So yes it is possible to have a secure service that doesn't collect IP addresses but yes the do have some limited data so you are correct.
I think it's great seeing other company's ship Steam OS I exclusively only play games on my OLED Steam Deck since I bought it. Just simple download and play no issues but I am a outlyer I haven't used Windows in 15 years only Linux.
This just seperates it into a secondary profile but all apps in your main profile are already sandboxed as well the only apps that are not sandboxed are system apps such as Play services. But you could use the app in a work profile(shelter) under a seperate Google account that would add a bit more anonymity. But android default app sandbox could be more secure there are other custom ROMs that do just that making the regular app sandbox even more secure.
Here is more information on how each android app is sandboxed(except Play Services)
I think it has more to do with Matrix is kinda becoming the standard for secure open source messaging server but I do agree with you I would just use what works for you personally.
Same here hence my username on here its the same on all platforms