I am on Big Sur 11.5. Davif Fraser's recommendation to swith UAS off solves the problem. No problem with any cables! I have checked and tested them. it is clearly a Big Sur problem. The Internet has thousands of people complaining about this problem and Apple does not care!

Yes, thanks. It works.I did not howver get my data back! ☹️ It is certainly a Big Sur problem and Apple side-steps every report on the issue, saying it is not a Big Sur problem. I have reformatted other drives due to this huge Big Sur problem, thinking it was my drive. All the time it appears to be a Big Sur problem! I wonder when Apple will set this right.