(Solved) xrandr 1.5 with setprovideroutputsource failed with nvidia driver 418.56-2 on debian+Quadro P400

The distro doesn’t matter, the radeon stuff just is a bit rusty.
Try this for /usr/share/X11/xorg.conf.d/10-radeon.conf

Section "OutputClass"
   Identifier "Radeon"
   MatchDriver "radeon"
   Driver "radeon"
   Option "AccelMethod" "glamor"
   Option "ColorTiling" "false"
EndSection

Then use
xrandr --setprovideroutputsource 1 0 && xrandr --auto