Personally I just fixed bugs that rendered the game unplayable but didn’t introduce new features so it’s still fair and doesn’t give me an advantage over others

I.e. my games FPS was really bad, like 20fps at times b/c of high vert count, so I fixed it and submitted, but I’m not adding full features like proper health bars and new content

Basically it’s allowed but up to your judgement, just don’t go too crazy with the updates - simple bug fixes should be fine from my understanding! 🙂

If you want to ensure that you stay true to the game jam, you could always leave the original build up to download and just mark it as the jam submission or mark your bug fix update as such. That's what I did for mine when I fixed a couple unintentional exploits. That way anyone who prefers to judge based on the actual jam submission will still be able to do so