This is low priority there are workarounds.
The default gallery app could use an ignore/hide folder feature like the files app.
Properly organized albums from bandcamp loaded into the music directory make one folder each with only one image on the gallery app (the album cover).
This is only an example, you can remove the image from the folder and keep the metadata thumbnails but it's inelegant and happens for other kinds of directory that may come with an accessory image, sometimes one that may not be optional in the documents directory for instance. You can also use an alternative gallery app of course.
Envisioned feature: one option in settings of the gallery app allows to choose path to enabled directories, default would enable DCIM, Pictures and Downloads (Documents debatably).