When I exit out of the Minecraft app, I get disconnected from any server, world, or realm I was logged in to. It doesn't disconnect if I just turn off my device. When I re-enter the app, it takes me to a loading screen and then sends me to the menu.
I believe it also affects other tablet/phone type devices, and it affects 1.16.210 as well.
In previous versions, I could do things like go to another app and come back (usually) in the server. I think it's a bug because the 1.16.210 changelog says "Brought back capability to rejoin a server after it has been suspended and resumed", and unless I'm that bad at reading, I think it implies this is fixed... but it isnt