Pop Out Window - No automatic brightness adjustment

Why doesn’t “Pop Out Windows” have automatic exposure/brightness adjustment
Very uncomfortable with Pop Out Windows on other monitors…

Here is an example, you can see how the brightness changes on the main PFD (ND) and does not change on Pop Out display…

Is there no way to add auto brightness to Pop Out Windows? (If there is no way to disable it in MSFS).

Not in-sim, no. Honestly, pop-outs, multi-monitor, all the advanced display stuff is done pretty poorly and is an afterthought at best.

However… the nice guys at Simstrumentation have an instrument dimmer that works if you are using Air Manager for bezels, but it only supports some aircraft. Their Discord is very friendly and you could ask around there.