Seems like the boys at DiskWarrior have given up trying to support APFS, for the last three years they’ve offered the pathetic excuse on their website that the next version of DiskWarrior will support those file types. DiskWarrior works on & fixes (or used to) the Directory structure of HFS+ drives. I’ve lost track of the number of times it has salvaged a recalcitrant HDD. At least it still works with Time Machine drives.
There is another utility app that CAN fix Directory issues on APFS drives, that’s TechTool Pro.
Today I had troule when Time Machine refused to make a backup, saying there was an unexplained issue with the destination drive. Aha, says I! Time for DiskWarrior. It tried but then went on a go slow when it consumed 15.5 GB of my 16 GB of RAM in the task. So I stopped the app with the Time Machine drive partially fixed but unmounted. Disk Utility was unable to remount the drive, so I disconnected the USB cable & reconnected it. I then logged out, & back in again, this freed up some more RAM. I decided to give TechTool Proi a go at it, but it refused to unmount the now-mounted drive.
Right. I opened Onyx app & freed up some more RAM then gave DiskWarrior one more try. It was able to unmount the drive, make its repairs & remount it. After which Time Machine was once again able to perform its backup duties.
The main reason I prefer Diskwarrior over TechTool Pro for fixing Time Machine drives is because it’s much quicker at doing the job. But DW can’t work with APFS drives whereas TTP can.