Okay, thanks Jason! I did end up trying a few keys, but they all ended up failing, so I moved on. I found a slightly older UNencrypted backup that I’m slightly happy with.
Jim, for some reason, my “Online Backup for WordPress” backups stopped coming to me back in November. I had been so busy that I didn’t notice…until now. So when I went onto my profile, it turned out I didn’t have any backups on the site, and it showed me as never having backed up my site.
So, I didn’t have the option of clicking the “show encryption key”.
You better write that key down!