I use an iMac with BigSur OS and I use an external hard drive to store my files. I use Time Machine for backing up. Recently my external drive failed (the iMac is OK). I tried to restore the files that were on the external drive using Time Machine, but there is a problem. When I enter Time Machine, I can see the external drive listed, but it’s greyed out and not allowing a Restore. Is it possible to get these files back?