Spotlight privacy on former Time Machine drive

I had assigned an external raid to be used as a Time Machine backup for a single time use. I've since removed the raid from being a Time Machine drive. But for some reason, Spotlight won't let me add folders from the raid into the Privacy tab. I get the "Folder Name is a Time Machine backup folder. You can not add it to the privacy list."

The raid is no longer assigned as a drive in Time Machine. This is on my 2017 5K iMac on 10.15.7.

Anyone know how to solve this?

Thanks!