(also affects 1.20.10)

Steps to reproduce:

1. Get to a high place while normally flying in creative mode
2. Equip an elytra
3. Stop 
4. Stop normally flying and start using the Elytra
5. Try to go back to normal flight

Expected result:

The player goes back to normal flight mode

Actual result:

The player continues flying with the elytra. However, pressing (A) or (B) does not accelerate the player upward or sneak, instead moving them up and down at the speed of creative flying. If the player lands in this bugged state, they will return to normal flying.

Also, yes. The player can sneak or sprint while using an elytra as well. Sneaking while flying and then landing will cause the player to enter a regular crouch.