Time machine backup location greyed out

I purchased an external SSD to start using Time Machine and it seems to be making backups just fine. I can see them if I open the external SSD and browse the contents. But if I click on the Time Machine icon and choose to browse the backups, it opens the browsing window but defaults to desktop as the location and the actual external SSD location is greyed out?

So I couldn't actually choose a backup if I wanted to do so? If I browse the backups and highlight one of them within finder, it asks me if I want to go to Time Machine and then of course I can't open the SSD to browse the backups. The SSD is formated to APFS, which I believe is the correct formatting.

Can anyone shed any light on this? I have done some searching here but the results all seem to be about the actual backups being greyed out rather than the location drive as in my case. Thanks.