a lot of my external drives have this error Could not mount “BUFFALO 3TB”. (com.apple.DiskManagement.disenter error 0.)

I have also tried everything in this thread and ending up with nothing.

I have a Drobo 2nd Gen connected by firewire or USB. Have tried both. The Drobo appears on the Drobo Dashboard and, most importantly, appears in Disk Utility. However, it remains in grey. Same errors as on this page when trying to repair disk and same error when trying to Mount the drive.

I have also tried to build a virtual machine with parallels and an old version of Mac OS but that took a day off my life as Parallels ultimately had to rely on the mounting of the disk in Catalina first before passing it along.

Any more thoughts on this?

So my solution above works to get the OS to let you access the drive. The problem is my drive has a corrupted catalog so there are some parts of the time machine backup that i couldn't access. The drive will have to be reformatted.

That being said there is a hidden gem of a macOS app that is a miracle worker. I've used it to recover many damaged HDD's. Even drives that GeekSquad and other computer repair companies said was a lost cause other than paying a data recovery hundreds or thousands of dollars to recover. I was able to do a deep scan using this program and recover pretty much app the files. Though some are no longer in their folder hierarchy. But not having lost thousands of photos made it well worth it.

Its called DiskDrill Pro by CleverFiles DO NOT BUY THE ONE IN THE MAC APPSTORE!!!! go to the Clever Files website and buy the Pro version. This app is GOLD if you need to recover a damaged HDD. Though I have had one, and only one HDD that it couldn't read. The icon should look like this.

While I wrote the above, DiskManagement gave it another try. It wanted to rebuild the B-tree catalogue but failed. When reactivating the disk it encountered Problem -69842.

Now what?

this worked! Thanks!