How to stop screen mirroring in Dual monitor in SDDM lock screen in open source driver?

I am using open source driver. I have Dual Monitor. If I start pc, at login screen I see screen mirroring of both monitor. But on propitiatory driver, no problem. How to fix this?
Here laptop monitor which is 1366x768 is mirroring the external monitor 1600x900. So, It is scaled up unproportionately.

❯ xrandr | grep ' connected'
eDP1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 340mm x 190mm
VGA1 connected 1600x900+1366+0 (normal left inverted right x axis y axis) 430mm x 240mm