Gallery appears not to be working with ftp as share enabled

[Omaha2002]

Steps to reproduce

1. click gallery icon in menu
2. blank page
3. after a long time previews appear

Expected behaviour

immediately showing previews of pictures that are local and a longer time before ftp or slow share pictures appear.

Actual behaviour

Blank page for minutes

Nextcloud version:
16.0.4

Nextcloud.log shows it's trying to find all pictures in the FTP share, obviously very slow.

possible solution: Maybe exclude external shares from creating previews in Gallery app?