I have 2 SSD HDs with photos. One can be Added to Lightroom. But Lightroom will only allow the other to Copy or Move. How can I get the other to allow me to Add the photos to the Catalog.

I'm using Adobe Lightroom Classic, 8.3.1 Release, (I don't use the cloud).  I just plug the SSD in and hit Import, but the only 2 buttons that are active at the top of the screen are Copy and Move, but Copy as DNG and Add are grayed out.  The first SSD that I use works just fine to Add photos to light room, but not the second one. 

Lightroom will use multiple drives.  What Lightroom are you using?  Each does it differently.  And how are you adding the photos?  What are your steps to do that?