MyCloud Mirror 6TB (Gen 1), physically removed, can't access + prompted to be reformatted

Newbie here and apologize if this has already been asked. I took out one of the drives, hoping I can access it through my Wavlink external HDD USB-connected reader.

Once connected, it says my HDD needs to be reformatted before use. Obviously I have data in them and didn’t click on reformat.

So, do I have to reformat it before use? Or does it just wipes the HDD clean?

Thanks in advance everyone!
-Calvin