@enzogianvittoria - ok, so some GOOD news...
someone mentioned what may be the problem & it was.
What browser are you using & what add-ons/extensions do you have on it?
It turned out to be the Grammarly add-on on Chrome that was causing my issues (I think) because I went to another Chrome person (I have about 6) that didn't have Grammarly on it & it FINALLY worked. I've been able to upload videos now since yesterday.
Also, if you use Awesome Screenshot, which I highly recommend for all sorts of things, & you can take a SS of what you see, that may give some of us a clue too.
Lastly, are you on Discord?