Hey, Yes you can submit a scratch game if it is uploaded on scratch.mit.edu
You can upload a project to itch.io which just contains a description. When you create the game page, you can add the scratch project link in the description.
When the jam starts, you can click submit and choose your game project on itch.
I removed your other topic showing 3D object because it is not related to the jam. Please only share things for the jam when the jam has started. If you want to share other things, feel free to join the discord server. https://discord.gg/pYCh5Nuwu4
