Time Machine Read-Only Error

Unfortunately, before I saw your reply, I ran Disk Utility on my Time Machine disk and it said it had become corrupted and could not be repaired, which was really odd because it had run perfectly only maybe about 15 minutes earlier, so since I had a complete SuperDuper backup from only two days earlier, I bit the bullet and reformatted my Time Machine disk and then TM successfully ran its "first" backup on the Time Machine disk. So I guess I will never know what caused it to become corrupted, because after Disk Utility reformatted the disk it said the disk was fine!

I guess the Time Machine's explanation that the disk somehow had suddenly become "write only" was a red herring. I have never written on this disk - only the Time Machine program wrote on the disk. Fortunately I run Time Machine and BackBlaze constantly and backup fully to a SuperDuper disk every Sunday, or I would have been panicked. "Not my first rodeo."

Thank you for your kindness and interest in helping me. I just replaced my mid-2012 MBP with this 2020 MBA M1 a couple months ago.