Hi,
Just found spacedesk looking for a solution for the same problem with MS Teams with a 43″ 4k monitor.
I also have to use some old software that keeps maximizing when interacting with it, and on a 4k monitor gets annoying really fast.
What I really wanted to find is a virtual display driver that would use a regular window as a secondary monitor. Searched everywhere but can’t find anything like that, spacedesk with a local viewer seems the closest to it.