Hey there Wecannotusethis,
We understand your FaceTime video feed is freezing, but the audio is fine. We'll be happy to help.
The best steps for issues like this can be found here: If FaceTime isn't working on your Mac
Even though your connection speed may be good, it's possible the connection may still be related. It may be on the other person's end. We also recommend testing with a different connection on your end to help isolate.
Another isolation step would be to use a new user account. This will let us know if the issue is system-wide or isolated to one account. Reference these steps: Set up users, guests, and groups on Mac
Cheers!