Similar to MC-229 but that says it was fixed. This happens in 1.21.4 and probably all the way back to when F11 became a thing to toggle fullscreen.

Steps to Reproduce:

1. Open video settings
2. Scroll to the Fullscreen option
3. Keep it on or off, doesnt matter
4. Press F11
5. The fullscreen option will say the reverse of if its in fullscreen or not
6. If you reopen the video settings, it will fix itself

In some older versions, eg. 1.16.5, you have to turn fullscreen off at the same time you turn it on with F11 and sometimes it will do it. Also why cant i add that to affected versions list? Can a mod add like 1.16.5 but like as partly affected?