Ehrenburg

This problem seems to be caused by a wrong placed "!" in the "player.animation_controllers.json" file.
Removing the "!" on "first_person_walk" : "!variable.bob_animation" to "first_person_walk" : "variable.bob_animation" solves this problem.
Then the bobbing toggle works again normally.

The mouse cursor leaves the game window in windowed mode.

This problem appears, when certain programs/games are running at the same time (or in the background) while playing Minecraft (Bedrock).
This problem also appears under the same conditions/circumstances in Roblox (also from the Microsoft Store).
Minecraft Java Edition does not have this problem btw.

For me, the game Overwatch is the reason of this problem. (I always play MC during the queue time.)
For other people with the same problem, may other programs/games/background processes are the reason of their problem.

The appearing taskbar problem in fullscreen mode can be solved by disabling EdgeUI.
But the mouse/cursor is still leaving the window when i play Minecraft in windowed mode (I only use one monitor).
I already tried a lot of things, but sadly nothing works.

Surprisingly, this problem does not exist for the Minecraft: Education Edition (1.14.31).
But afaik Minecraft: EE is a Win32 program packaged as an UWP app, but the normal MC BE is a full UWP app.

With this information i have good reason to believe, that the UWP app format (also known as Windows Apps) is the reason of this problem and it may have to be addressed to Microsoft too, and not only to Mojang.