Facing the same problem with the CAD-style app drawing its contents using Metal. To save resources the app redraws/animates the contents only when a change has occurred (like changing a radius of a circle). Apparently, macOS interprets this behavior as not requiring too much GPU power and keeps the display attached to the integrated GPU. I suspect it also optimizes some resources used for blitting into the integrated GPU (like releasing some buffers after some timeout), so there are annoying redraw stalls of 1-2 seconds, especially after 10-15 seconds of inactivity.