Exclude ext. drives from displying photos

Hi, @Alexander3807335978sn, I know this is not the answer you expected but since you are on the Mac platform, I cannot encourage you enough to get HoudahSpot. It will do EXACTLY what you want, and a lot more. I have been using this for years, and this is what I go to when I want to find anything.

BTW, I also was having the same issue as you: files on one drive, backup on a 2nd drive, and didn't want to see both. I wrote to the developer if it was possilbe to split the various drives so one would see one block of (found) files in one group and each subsequent found files also separated groups. By the next update (a couple of weeks passed), it was there. It completely solved my issues.

1: I speak as a Windows user, but I believe that Bridge shows all connected drives though it does not display their contents by default. You would have to "browse" within the drive to see its contents.  If this is a serious issue for you, given that Drv. B is an external drive why not simply switch it off?  Since it is a backup drive you surely won't be using it all the time. It will then disappear from Bridge's view.

2: To see all photos in all folders, select the highest level parent folder and then choose View>Show Items from Subfolders - better still, create a custom shortcut.