Many game jams I've seen will specify whether or not this is allowed, but this one doesn't seem to, so I was wondering if it's okay to e.g. download sprite assets from itch.io and put them in my game? Either way I'd make sure to give credit and a link to the assets used, but this would definitely save me some time and make the game look better

Yes, it's totally fine to use any pre-made assets. Sorry, we hoped that "any software, tool..." rule in the description answered questions about using assets but it probably wasn't clear enough. We appreciate all the feedback and we'll clarify better in future jams.