How to uninitialize an external disk in MacOS
Is it this disk ?
/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *31.0 GB    disk2
   1:           Linux Filesystem                         718.2 MB   disk2s1
   2:                        EFI ARCHISO_EFI             68.2 MB    disk2s2
   3:       Microsoft Basic Data                         307.2 KB   disk2s3
                    (free space)                         30.3 GB    -

If yes you can do :
diskutil erasedisk jhfs+ &quot;Free Name&quot; gpt disk2

You can try
diskutil umountdisk force disk2

Then retry
diskutil erasedisk jhfs+ &quot;Free Name&quot; gpt disk2