every time i try to start it i get: failed to load mono. how can i fix that?

Welp, officially disappointed in the developers.
Fwiw, they aren't very active on steam either, nor do they reply to emails.

Failed to load mono is a unity issue, I'd verify/repair or reinstall.

If that doesn't work you can try to install mono 64 manually here.
https://www.mono-project.com/download/stable

I think they fixed this on September 15th, so you might be behind on a patch if you're using offline installers and only installed the base.