U2720Q, Apple, switching input devices

@robcos  I doubt this is configurable.  This would be a firmware-level design decision in the display, and different displays behave differently in this respect.  There are pros and cons to each.  The downside to this display's approach, as you've noticed, is that you can't see what your laptop is displaying in that portion of your overall desktop area when that display is using another input.

But the downside of the opposite behavior that you're requesting is that if the display disconnected itself from the inactive input, your laptop would pull everything onto its main display, and then it would NOT put those application windows back ONTO that display when you switched the input back.  I've seen complaints from other users about that exact behavior when using displays that behave the way you wish yours did, because having to manually reposition all of their application windows onto the external display all the time gets irritating fast, especially if they only need to switch inputs momentarily and/or frequently.

This issue is especially prevalent among people who use KVM systems.  The ones that are generally well-regarded are the ones that deliberately continue advertising the presence of the attached display(s) even to the inactive source system(s), rather than disconnecting them and causing the inactive source to consolidate everything onto the built-in display.  The ones that behave as you're requesting tend to get negative reviews for doing so.

Of course both sides of this discussion have merit, and different use cases will undoubtedly benefit more from one design over the other, so it would certainly be NICE if this behavior were configurable, but I've never seen a display or KVM that offers that customization.