I switched from stable to git and since then the Steam overlay is not working
anymore. I tested it with two games (Rust and Worms Reloaded) but could test it
with more if needed.

With not working I mean exactly this. The message that it's enabled and you
have to type shift + tab to open is doesn't show up, also shift + tab or F12
(taking screenshot) does nothing.

I may try to bisect it later but am not sure if I'll find the time.