Adding to the confusion. Sometimes I get through 25% of the backup (~500G) and others I get 50% before the backup fails

Same comment as above however after the daIL. There is a backup on the drive

Eureka, now if we could get Time Machine to work

No, it didn't. I am on beta 4 as well

I spent some time searching online and found the following link below: https://forums.macrumors.com/threads/time-machine-the-file-could-not-be-backed-up.2304725/ One of the solutions in the link is to make sure and exclude Time Machine from backing up your OneDrive folder; it seems to work. at least for the initial backup of my system I wonder if other "network" folder systems have the same problem. I have Box, but I had been excluding that from Time Machine before these problems began.

Same

I finally got 18.1 Beta 2 to load on my iPhone 15 Pro, and here is what I had to do. I put the phone into recovery mode, and when prompted, I connected it to my MBP (M1). It asked if I wanted to update or restore, and I responded restore (make sure you have backed up your phone); my phone was restored to iOS 17.6. NOTE: I DID have Apple Developer 18 betas enabled when I went into recovery mode, and immediately after the iOS install of 17.6, the phone updated to 18.1 beta two, which it did. This takes a while because the restore process removes all of your data ( and apps you installed) and restores from the backup. P.S. My phone just notified me that 18.1 Beta 3 is available for download. Hope this helps