Login Screen (SDDM) - Play video background - ERROR: GREETER: High-DPI autoscaling not Enabled

A few years ago I managed to play a video as background in the login screen (SDDM). Unfortunately I forgot how I did it and I can't find any instructions that work.
How to add video background to sddm login screen
This guide is not complete, I get this error message:

Code:sddm-greeter --test-mode --theme /usr/share/sddm/themes/breeze
GREETER: High-DPI autoscaling not EnabledLooks like the "autoscaling" function is not active.
How do I activate "autoscaling"?