I also encountered the same bug.
When I try to connect to servers or Realm, I get an error "You must be connected to Wifi to play with your friends."
This error message usually only occurs when "Settings > General > Profile > Use Cellular Data" is turned off, but it has always been displayed since the update v1.16.100.
Everyone who doesn't have Wifi continues to be unable to play in multiplayer. Due to this critical bug, small communities are on the verge of extinction. Please Fix it immediately.
sorry
It seems already fixed by 1.16.101.
thank you