It's the first time I participate to a game jam where the theme is proposed by participants, and 95% of them are just bad.
There is a lot of themes that were already used in previous LDJam, pandemic related themes (got Quarantine more than a dozen of times), time, gravity, and space everywhere.
Some classic light and dark, death mechanics theme
Way too much Reverse something, negative something, that's just not original anymore
But the themes I hate the most are the one that limit your inputs (only one button, indirect control), your mechanics (can't move, can't touch the ground, limited resources), the world art (everything is cube, no color), the genre (VR, fps, rts) or the levels (only one level)
A good game jam should have an inspiring theme, for example, Butterfly effect, Keeping a promise, seasons, Hell, red fox, moon, four elements.
This way everyone can choose their own genre, you can tell the story you want, and more importantly, you can have the mechanics you want. The theme is just a way to unify your game, it should not prevent you from doing a good game that you like.