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.
sannyo
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