com.apple.DiskManagement.disenter error

On my Mac Fusion
I am working with Mac OS Catalina on an external disk partition APFS
My extrenal disk is a Samsung T5 with 3 partitions (1 APFS and 2 Mac OS extended)
I cannot see on the desktop the Macintosh HD with Big Sur installed.
This disk is mounted.
If I unmount it and try to mount it, I have this error
com.apple.DiskManagement.disenter error -119930868

Can you help me?

Thanks