I'm almost certain that there aren't any restriction, but practically, it really depends on what you're aiming. If you want to win a prize, I'd recommend you take some weeks to learn something like GameMaker, Godot or Unity, just so you get more freedom to create functionnality, and can directly use basic tools such as camera or instancing, which would take quite some time to recreate in Scratch.
If you just want to get better without learning too much new stuff, just go for Scratch. It has quite some potential even if you're not GriffPatch.
Edit 1: [made my post more precise]


