>click "Get New Plugins"
>look for the"Smart Video Wallpaper Reborn by luis-bocanegra" and click install
>add your videos, set them to loop and hit apply
This is the plugin's github page in case you want to build it from source:
https://github.com/luisbocanegra/plasma-smart-video-wallpaper-reborn
https://steamcommunity.com/sharedfiles/filedetails/?id=2434025795 this guy has some great blue archive L2D wallpapers, if you already own Wallpaper Engine on steam just download these, navigate to where they were saved and copy the MP4 files
Oh, and you can set the lock screen to have animated wallpapers too!
you can do animated wallpapers in KDE!!!