I received your email with the test project. I used your repro steps with the sample project. When switching between the two I’m not seeing any FPS drop. Each stays at a consistent 62 fps (the locked max FPS). I even used the console command and set t.MaxFPS to 120 and I see a consistent 100 FPS whether an instance is in-focus or not. I tried to capture a video with both screens, but wasn’t able to with the tool that I have (Snag-It).
Even using Stat Unit, I’m seeing consistent behavior across both instances of the exe being opened.
I’m open to test any other steps you may have.