[junon]

In the pathological case, the steam overlay needs zero effort to "implement". It works out of the box in most cases when the application is launched via the Steam launcher.

[schemescape]

It only works for DirectX, OpenGL, Metal, Vulkan: https://partner.steamgames.com/doc/features/overlay

It also uses heuristics to find the right window that can lead to issues. Not a common problem, but one I unfortunately ran into :(

[int_19h]

What other rendering backend options are there even these days?

[schemescape]

Electron and other HTML runtimes are what I had in mind. I’m not sure what renderer they use, but it’s something else.