The rules are clear, don't use anything you don't own the rights/have permission to use for the purpose of this game jam.
"You can use any art, audio, code, or tools that you have the legal right to, but you shouldn’t make assets ahead of time that would be specifically used for this game jam. If you previously made an asset that ends up being good to use for the jam, that’s totally fine. Just don’t do any “prep work”, heh.
You can use any assets available online! (Free assets, purchased asset packs, etc - if you can legally use it, it’s fair game!) I also request that you don’t use generative AI to produce art or music for your game."
Also, grabbing music from existing games that took thousands of hours to make — compared to the few weeks we have at our disposal during the jam — is just incredibly unfair. I'm sure you can understand why.