Put the summary of the bug you're having here

What I expected to happen was...:
Previous Java games should work. Also the newly installed Terra Swoop Force, which worked YESTERDAY.

What actually happened was...:
NO PREVIOUS games work. I think a plain, new world, default, works, but I don't use those. I STRONGLY SUSPECT the new screen option, and the programming behind it, are the issues. As with Bedrock, this is being launched before adequate testing, and is wreaking HAVOC!

Drag Data Pack  is NOT explained! What DO you want here???? I see FOLDERS at Roaming/.minecraft/saves   . I do not see ANYTHING titled Data Pack! So QUIT the mumbo jumbo ancient jargon. Use RECOGNIZABLE words!

Steps to Reproduce:
1. Please post, in an EASILY accessed place, what is happening.
2. Fix wording to make sense as to WHAT FILES, FOLDERS need to go, WHERE?
3. If ONLY DEFAULT works, then have a pop up, at that WINDOW, that SAYS ONLY DEFAULT WORKS.