Thanks for the suggestion. I should have clarified that the standard sleep() function takes seconds, it's just to minimize code amount. Sadly, this does not resolve the issue.

Confirmed: I have this issue when debugging an app that makes an OpenGL / GLFW window in XCode 16.2 / Sequoia 15.0. It's certainly a bug, and it's dreadfully confusing, because I'm never sure which app is the one I'm debugging. As a workaround, sleeping the app in the main function for 1 second, before initializing the window, will prevent the duplicate app launch. The response from official Apple developers is concerning. Is there a higher-up developer to whom this issue 'will really matter'?

Looks like MacOS Montery 12.3.1 updated the video codecs. Perhaps the problem is fixed.