When we attempt to change game mode via commands it will only change the mode for whoever enters the command. (personal gamemode)
To add further to our evidence, I too have been experiencing this issue.
The test cursor happens on realms and locally. Yes, I am using add-ons.
Here's a video further adding to the issue. I cannot change the game mode on realms but I can on my local world.
Can confirm as well, if you set "gamerule recipesunlocked false" the category tabs come back. FYI I am not using experiments.