> I can guarantee you any gamedev worth his salt will have used alt-tab at some point in the game's development on windows.

Not exactly a repeatable testing framework, that.

> You seem to be trying really hard.

I almost strained a typing finger! /s lol

> Most devs are using cross platform graphics APIs. OpenGL/DirectX/Vulkan. Alt-tab breaking is likely an OS issue.

All the OSes seem to suffer from it similarly. More likely an issue that even the cross-platform graphics APIs rely heavily on shared memory buffers and most games depend on code written in languages which aren't strictly memory safe. Sharing a memory buffer between CPU and GPU (or even just multiple CPU cores) is quite difficult to do safely under all possible circumstances without proper language support.