It's working for me and I have a July 2019 13 inch MacBook Pro- I don't really use ethernet that muchThis is hitting me pretty hard...YouTube is not working in Safari on Big Sur Beta 10 (on Intel) no matter what I do.
Turned off VP9 Decoding
Turned off Content Blockers (temporarily and permanently)
Tried Safari Technology Preview
Tried Private Windows
All other browsers seem ok...
USB ethernet doesn't work either.
I don't have any extensions in Safari, not even a adblocker.I have had this as well, with Catalina. My guess so far has been that this is related to AdBlocker, blocking an otherwise playing Ad. A quick reload (CMD+R) helps.
And yes, it also happens with Big Sur