You need to upload a .zip file.
Viewing post in Runaway Russian - Mechanized jam comments
Hi Curtis
https://itch.io/docs/itch/integrating/compatibility-policy.html
As you can see, publishing a .zip file is usually better than a .7z as more people can extract it easily. I have also noticed when publishing a game that my .7z files always had fewer downloads as compared to .zip.
Cheers