This issue has been hapenning since 1.16.100. I can't name the exact reproduction steps, but it happens quite often just by playing the game: local multiplayer or realms.

Loading indicator appear on opening a furnace UI or accessing inventory. You can still walk around and the game basically goes on, but you can't interact with any items and can't access the pause menu.

There is a chance that after a minute or two the loading indicator will go away and inventory will open, but usually only killing the application on the switch and restarting the game helps.

UPD: This has just happenned to me on title screen as well, attaching screenshot.