Usually i used the original windows image viewer to sort and delete my hundreds of screenshots from any games, and once they were deleted (not thumbnails), it was COMFORTABLE to delete them from steam, because all deleted screenshots were marked with a triangular indicator.

Some time ago i wanted to clear my screenshots again, but i have realized that in steam gallery i can't pick one, several or more already deleted screenshots, and now i can delete them only by clicking RMB on each of them...

https://imgur.com/a/Z6O5WBr

so will be good to fix it