Hi, I am having the same problem. iMac pro upgrading to big sur, cannot find the external Sandisk extreme pro disk.
But I think there is a temporary way to mount the external disk.
go to disk utility
find your external disk, click and choose the disk
mount (top right corner of the utility window)
every time you mount the disk, you need to do 1-3
Hope this helps. Wish apple developers can solve this issue asap.
haoyeah
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