How to set a custom dynamic wallpaper in Catalina?
There are 4 solutions to this problem. 


Easiest


select Catalina wallpaper (System Preferences->Desktop &amp; Screen Saver)
make sure the popup button has selected Dynamic item
close the System Preferences
locate your wallpaper, right click on it and select Services->Set As Wallpaper


Mid (requires tools) Remove Still images from dynamic wallpaper


recreate dynamic wallpaper without still images (remove appearance metadata)
dynamic wallpapers without still images will cause only one menu item to be present and it will automatically get selected
Dynaper has the Remove Still Images Helper tool


Hardest (but best). Place dynamic wallpaper into System/Library/Desktop Pictures/


disable SIP
reboot
open terminal and make System partition writable sudo mount -uw /
copy wallpaper with root sudo cp path/to/wallpaper System/Library/Desktop\ Pictures/
OPTIONAL: copy custom thumbnail (same name as wallpaper) with root sudo cp path/to/wallpaper System/Library/Desktop\ Pictures/.thumbnails/
enable SIP 

Hardcore 


use Xcode: attach to process com.apple.preference.desktopscreeneffect.desktop.remoteservice and Debug view hierarchy
find the incorrect popup button address
pause program execution
run command [0xaddress setHidden:YES]
resume program execution
modify wallpaper selection to Dynamic



Explanation:

Starting macOS Catalina the system prefers Dark still image on dark appearance. Due to bug 2 overlaping popup buttons are displayed. For images inside System/Library/Desktop Pictures/  the disableCustomPlacement is set to YES (this makes the other popup to be hidden) . All other locations will have this property set to NO (this causes 2 popups to be displayed). 

 Derived Properties:
     pictureChangeIsActive:  0 
     canSetBackgroundColor:  0 
     disableCustomPlacement: 0 &gt;