I would like to ask, given that the theme of the jam was published long before it began, does this prohibit the creation of the project in advance? I didn't find anything in the rules regarding this, or is it an obvious thing at every jam?

Same question here. I already started my game  😬.  I think for game jams with the topic already given, you are allowed to start early. Just a guess, I don't know for sure

I don’t think you’re able too, if you were there wouldn’t even be a “Jam Start Date” it’d just be “Submissions open till (deadline)”

Oops, ok then. I guess I'll have to submit something else for the jam.

To all of you asking, no you cannot make a game before the start of the competition. And the theme has not been revealed yet. It said that in the description of the jam. Geometric shapes is an optional aspect of your game but not the actual theme.

There is an additional theme its not just the shapes just FYI

From the page

"Additionally, a theme will be announced at the beginning of the jam period, and so you're encouraged to link that to your game as well!"