There should be no rules against the use of the scratch "engine" (you can use any game engine tbh), but i would consider using something different, something easy like Pygame for example, since scratch is not really made for game jams, and i have no idea how you expect to submit your game using scratch. But hey, it's your game your choice, this is only my opinion.
There isn鈥檛 any rule against Scratch as long as you don鈥檛 send the link to it as a Game entry, just compile it to WebAssembly using TurobWarp, + if you don鈥檛 know any Game Engines, I recomend watchin tutorials For Unity, Godot
or use a library to make games for Example SDL2, RayLib, or PyGame
