I have done several third party bandwidth checks from Salt LakeCity center to 50 miles north when 5g is in the top right of the phone and I still maintain 5g speed. This might be a tmobile issue but wanted to see if other users are experiencing the same problem on different networks once the phone says "5G"
The note 10 + 5G has major issues. Its a Samsung issue. its the GPS chip conflict with the 5G chip. So it doesn't know how to connect to the correct Tower also other minimal GPS functions speed test Google maps sometimes doesn't work there's no update insite as of right now it's been going on since August. Check the forums. One thing I just tried putting the phone in performance mode seems to be working. I've also turned off band 71 which is the 5G band and the 4G LTE 600 band and it seems to work all day. Maybe this will help you.