Media library thumbnails not always generated (especially in the flatpak version)
Besides being less helpful for users, this also makes Pitivi look unpolished in demonstrations. It is my remaining gripe with the Flatpak version: Pitivi somehow can't see/access the user's freedesktop thumbnails (generated by Nautilus or whatever) from outside the flatpak, and when inside the flatpak it doesn't generate them either*
*: unless (in theory) it is creating a proxy for a particular clip (from what I'm told, some of the thumbnails are "created during the proxy generation step" nowadays)
...so if Pitivi can't generate them normally (with the freedesktop thumbnailers) inside the flatpak, nor can it read the thumbnails generated by other apps... that means it can never show thumbnails in the media library, which means the iconview suddenly becomes handicapped (no point in having a bunch of icons without thumbnails with badly truncated filenames such as in issue #2333).
Medialibrary/freedesktop thumbnailing shouldn't require the use of proxies in theory, especially since some formats are "well supported without proxies" (and/or the user may elect to simply not use proxies for various reasons; that's the point of having a choice regarding proxies anyway).