While Scratch games are accepted in the jam, participants are asked to package their game in such a way that they do not have to be run through Scratch. The Turbowarp packager can be used to do this. Here's how:
1: In Scratch, share your project or download it using File > Save to your computer
2: Go to https://packager.turbowarp.org/
3: If you shared your project, choose "Scratch Project ID or URL" and copy and paste your Scratch project link into the text box. If you downloaded your project, choose "File" and upload your .sb3 file
4:You can tweak various settings in the Runtime Options field. This includes various enhancements such as higher FPS, interpolation, and custom stage size. If you want to use one of these, I recommend trying it out on https://turbowarp.org/ first to make sure it doesn't cause any problems.
5: Use the Player Options field to set an app icon, change loading screen settings, and other miscellaneous tweaks. You can also use the Input field to change the mouse cursor.
6: In the Environment field, choose "Zip", then click the "Package" button. This will download a zip file of your project, which you can use for your submission. When creating the Itch project for your submission, choose HTML for the "Kind of project", and upload your zip file. You can also upload executables for Windows, Mac, and Linux alongside your web build by changing the Environment setting in the Turbowarp packager and packaging your project again.
If everything went well, your Scratch project is now easily playable from Itch! If everything did not go well, feel free to ask for help. Have a nice day!