Accidental deletion from the vCenter inventory or overwriting during an ESXi upgrade. Articles - VMFS Recovery
Run esxcli storage filesystem list to see if the volume is recognized but simply not mounted. recover vmfs 6 datastore
The most critical rule is to avoid writing any new data to the affected LUN to prevent overwriting the remaining VMFS structures. recover vmfs 6 datastore
or force a mount if necessary:
Install vmfs-tools on your Linux system and use it to recover the VMFS 6 datastore: recover vmfs 6 datastore