I have a MacBook Pro 17inch with BigSur OS (v 11.5.2) and a new Samsung Smart TV (UE55TU7070U). Due to company policy, I can only connect my laptop to the TV with an HDMI cable. I tried 2 different HDMI dongles (neither official apple products) on 2 different MacBooks and all 4 USB-C ports on each of the laptops and the result is always the same. A picture appears for about 15 seconds and then it goes to a black screen. Every couple of minutes a white noise screen flickers on for a second or two.
I tried the same dongles and same HDMI cable with my Samsung Galaxy s10e and it works perfectly, loading the Samsung Dex. Which suggest the cable or dongles are not the issues.