Are we allowed to upload new builds after the submission time? Can I upload a webgl now? Because many guys don't have windows and can't play my game.

Yeah it's fine, as long as you don't add new features to the game.

Here's my game btw: https://itch.io/jam/wowie-jam-2/rate/551749

I'll try yours!

I've seen people add wasm builds after I mention that I couldn't play their game because I don't have windows. If you want to be save, try to contact Jonas directly about it.

Hey hey, minor bug fixes and creating new builds is allowed. 
Additional polishing, rebalancing and adding content is not allowed during the rating phase. :)

Cheers. :)