I think this is a consequence of your desktop being 18432 pixels wide. Each 4K monitor is 6144 logical pixels wide because of a custom Xrandr scaling factor of 1.6.
Turning off screens wouldn't fix it, only unplugging them might. But still this sounds like a GTK bug because modern Nvidia GPUs like yours should be fine with an 18K desktop.
I think this is a consequence of your desktop being 18432 pixels wide. Each 4K monitor is 6144 logical pixels wide because of a custom Xrandr scaling factor of 1.6.
Turning off screens wouldn't fix it, only unplugging them might. But still this sounds like a GTK bug because modern Nvidia GPUs like yours should be fine with an 18K desktop.