Downloaded dynamic wallpapers glitch
You have to put them in &quot;the right&quot; folder to make them work properly.
You can find all different rather complicated solutions including disabling the SIP (System Integrity Protection) with going into the Safe Mode and so on, but the easiest method that works (as of Big Sur 11.2.1) is to copy them to: /Library/Desktop Pictures folder for which you need only regular root rights:
So basically you do something like:
sudo cp ~/Downloads/Firewatch.heic /Library/Desktop\ Pictures

then you see them appear along with the original ones: