100GB seems excessive. If you’ve asked it to revert, then of course it will make those changes. Do you backup often, I would hope so if you’re using Unity.
I even keep my profile pics for social media on my PC and in the cloud with a 30-day trash bin, besides the social media themselves. Guess those weren’t your most precious 100 gigs…
Also, if Agent was able to delete a bunch of important stuff only through git, then most likely the project had .gitignore configured incorrectly and you ignored it.