The bug
The follow actions aren't cancelled after the gamemode switcher is opened:
Blocking with a shield
Preparing to shoot with a bow/crossbow
Prepearing to throw a trident
Eating/drinking food item
Using a spyglass
(List may be incomplete)
You can let go of the right-click button on their mouse, causing the player to stay in that current action unless a gamemode has been chosen.
To reproduce
Have a shield and hold right-click
Do F3 + F4, do not pick a gamemode yet
→ ❌ Your player is stuck in that action, and you can let go of the right-click button and observer that you are still blockingVIDEO
Hi there!
I can confirm.