Just upgraded to Sonoma.. and No ... the Time Machine disk is not mounting nor repairable from disk utility.. again.. I actually bought a new disk after my upgrade to osx 13 I think.. because of the same issue.. And as I read here it is not a new issue. It is a pity apple is not able to fix this problem. This bug/issue is a huge waist of time and money. How to get all my old backups back and have my disks run again? they just do not show up and/or mount/repair. I tried most of the suggestions mentioned here above. Perhaps I let a windows machine repair the disk.. hahahahaha .. and when that doesn't work erase.. when that works.. (?)