Scale of primary screen is used as a base for any secondary screen as well
I have a laptop with a screen of 3840x2160 pixels on a 13" physical size. To make things readable I set the scale to 200% on the display control panel. Everything fine and dandy
But at work I have an external monitor of 1920x1200 pixels on a 23" physical size. On the display control panel the scale for that monitor is kept at 100%, but it is unusable as it is way too big, as it feels to be 200% scale rather than 100%.
The primary display is the 13" scale 200% monitor.
Setting the primary display to the external 23" monitor does work as in the external monitor is not scaled, i.e. not resized way too much, and the laptop is correctly scaled to 200%.
I'm not so sure if that's a g-c-c problem or an underlying component, I hope it is not too much burden to do the triaging.
I would be more than happy to get debugging, if I get some instructions. I'm a professional developer and I have been using GNOME and linux for decades, so I hope I can be useful