Big Sur - external discs not mounting

This is what fixed exFAT partition is not mounting.

Fsck was doing some work forever on that partition. Using ps aux | grep fsck showed the drive being busy.

sudo pkill -f fsck worked and the drive basically auto mounted.

Found the answer on stack exchange but can't link it due to saying "https://apple.stackexchange.com/questions/293390/macos-cant-mount-exfat-external-drive" is not a permitted domain on this forums.

Had a similar issue. 2-3 USB devices working properly on any computer stopped working on a student computer. Struggled with searches then in Security I saw the student had the Firewall on...... Tried to turn off and apparently she made a setup to block USB connections !!!!!

Since then I've been able to connect USB devices again. Took me an hour to figure this out....... And student next to me staring at her computer all the time.

An alternate "solution" if you're a numpty like me:

If external drives are mounting normally in Disk Utility but not appearing in Finder, they might just be hidden from view in Finder. I didn't realise that the little arrow next to "Locations" in the sidebar of Finder windows had been minimised, so any external drives were invisible even when mounted.

This isn't a solution, just another situation people might encounter.

Thanks Billinski, your method worked for one drive: partitioned, one partition shows, another does not!), will try additional drives. I agree with earlier commenters, Apple should disclose this issue at least and have support for this issue. Most of us are quite loyal to the brand and have spent thousands of dollars on Apple Hardware and don't deserve the lack of transparency.

Have and iMac, MacBook Pro and Mac mini running Big Sur 11.6.5. New seagate 8tb external drive formatted in disk utility works great. Until it's moved to another computer. MacBook Pro and mini will not mount. Cannot see the drive in disk utility on any other computer. Same issue when plugging in to iMac running high sierra or mac studio running monterey. Only works on the first iMac. An hour call with seagate and Apple turned up nothing. They are baffled. Reformatted drive on original iMac to ex fat, then apfs, then back to journaled, doesn't make a difference. I had another new 8tb seagate drive formatted on the high sierra iMac and it works on every computer. There is something wrong with Big Sur.

I just updated to macOS Ventura beta 1 and now my external drive won't mount. I can see it in Disk Utility, but when I choose mount I get an error: "Could not mount “NIKON D3200”. (com.apple.DiskManagement.disenter error 53249.)"

THANK YOU THANK YOU Billinski !!! I was panicking, sweating and going through a rollercoaster of emotions when my external wouldn't mount. thank goodness for this thread and to ty to Billinski !

Actually if you run in terminal command like "ps ax | grep fsck" in the Terminal, you will see that filesystem check is already running (and checking your device). And this is why clicking on "mount" or "first aid" will return error, because it on repair right now. And when it finish disk will be automatically mounted and will be working again. However it can take a lot of time and for my 2 TB WD disk the time was about 2 hours. So be patient and let the system check your drive fully.