It looks like browsing and previewing pictures on removable media is not supported in any meaningful way.

I am able to see folder structure and file names. I cannot see thumbnails or metadata. In the context menu for a file, the "Open" and "Reveal in Explorer" options simply don't do anything.

I have tested this with an Android 9 device in MTP and PTP modes. I also tested with a plain old USB flash drive.

No matter how slow it may be, I want Bridge to fetch thumbnails for all my photos and browse them before downloading or deleting any of them. I do not want to transfer all pictures to my computer to be able to go through them.