Good morning,
Currently I still have the video thumbnails in Dolphin on Artix OpenRC XFCE.
My personal recipe for adding Dolphin to Artix xfce:
sudo pacman -S ark dolphin kdegraphics-thumbnailers kimageformats oxygen-icons qt5-imageformats
N.B. I am using oxygen icons and Adwaita themes in xfce4-settings-manager
I add kim4 (AUR) which is quite old, but very practical :
yay kim4
1 aur/kim4 0.9.8-2 (+3 0.00) (Installé)
Kde Image Menu to compress, resize, convert, rename and much more