Problem making external HD visible in Finder; demands a password instead

I have a recently purchased a Scan Disk ARMOR external hard disk for use as Time Machine.  This week, it stopped being visible in Finder, and every time I wanted to access it I was asked for a password.  It was clearly a password I had used for something previously because I had the option of viewing a Hint (which I remember doing a long time ago, but not for this HD installation and it obviously wasn’t of any value because I couldn’t recall the actual password from it!

I couldn’t access via Time Machine, and connecting the HD to my PowerBook instead brought the same result even though I have not previously used the HD on the PowerBook.

The HD, or any password associated with it, does not appear anywhere in my System Settings > General > Passwords.  How can I remove the Password request window so that I can make it visible in Finder and therefore open it?  And if I wished to erase and clean the HD to start again, how can I do that if the HD is not visible in finder?

My iMac is running Ventura 13.7.5