Unlocking Crucial X8 backup password for iMac data recovery

My 2024 iMac had some problems and went into the dealer, who carried out diagnostic tests and then wiped the disk and reloaded the software. When I came to set up the computer, I was asked to transfer my backup data. I have two backup devices, one is a Crucial X8 and the other is a Passport for My Mac. I backed up my data using Time Machine on the x8, the Passport also recorded data.

When I nominated the X8 for data recovery I was asked for a password for the X8, but I had no idea what this was. The hint that was given was I think was that it was the sign in password for the Mac, but this didn't work. Fortunately I got most of my data back, but I need to unlock the X8. I had set up different passwords to log into the computer, but these didn't work either. Any ideas greatfully received please.

[Re-Titled by Moderator]

Original Title: Unlocking Backup data