Konqueror
From NixOS Wiki
Since NixOS makes it easy to run individual KDE applications without running the KDE Plasma desktop manager, one can easily install Konqueror as a file manager; but (as of NixOS Stable 22.11) it won't show thumbnails (which it calls "preview icons").
The fix (again, as of NixOS Stable 22.11) seems to be to install these packages in environment.systemPackages, in addition to libsForQt5.konqueror:
- ffmpegthumbnailer
- libsForQt5.kdegraphics-thumbnailers
- libsForQt5.ffmpegthumbs
- libsForQt5.kio-extras