Give a try on displays of different sizes, like a 13/15 laptop with 27 external.

The best I found is 21 and 27, just need to find a decent 21 modern replacement that is not low contrast LCD.

Even better if you can dim the brightness of the secondary display.

With the notebook display I can just use the brightness shortcut of my keyboard (both on Logitech MX or my Keychron one).