Hey, I need help :(

I was tinkering a bit with Collabora and Nextcloud Office. First it worked fine, then I noticed that only SOME office documents were opening in browser, some were just downloading.

After tinkering more, the situation is completely broken now: All files, images, videos, office documents are listed as "unscanned" in the web interface. And they don't render in browser, but get downloaded right away when you click. (Also no "view" option in the three-dots-menu).
occ does NOT see unscanned files (tried occ files:scan --unscanned). A full rescan of files also didn't help.

Does anyone have any idea?

Turns out, the "unscanned" was just a tag from some app. I've remove those. But still the main issue remains: No picture has a thumbnail, all pictures download instead of rendering in browser

Cause found: App formvox broke mimetypes for me. Disabled, it works again. Additionally, I had an incomplete list of mimetypes in db, fixed via occ maintenance:mimetype:update-db