The question breaks down into two:
- Is it even possible to create a Windows app with an opaque (not fully transparent) background that can be overlayed on top of other sources in OBS? Any examples of such apps?
What I mean is:
- If yes to (1), then what GUI frameworks (preferably C++) can be used to reach this? I know for sure that WinUI and WPF can't do it. Dear GUI, Sciter, Cegui?