Scratch is allowed for any jam that doesn't say you have to use a specific engine. i'm also making a game using scratch by the way, it's nice to know i'm not the only one lol.
i'm using regular scratch, because i also want to share it on scratch. i use HTMLifier to turn it into HTML. and yes, the only thing that holds you back on scratch is framerates. some people think scratch is a "baby language", while basically anything unity or godot can do can be done with scratch (at very low framerates)