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Well, I believe so but you would run in to problems when trying to submit the Game on Itch.io, you would need to put a url with the Scratch Game
in the Description. But you are free to use whatever you want. Quote from jam rules: "Apart from that you are allowed to use any game engine or framework"
And Scratch is a sort of Game Engine

thank you concon7557, I was unclear so this helps alot

You can't link a project in a describiton or you will get disqualified. On github is a program that will convert scratch files to HTLM5 files which can be uploaded.

HTMLifier (sheeptester.github.io)

Almost correct. A link to an external site disqualifies you. There are 3rd party tools that can help with getting a file to put on itch.io.