If you created the folder environments.d, then you did it wrong; that directory doesn’t have an s in it. It’s $HOME/.config/environment.d. That will be why it didn’t work. Also, you likely have to at least restart Steam after making a change there, because those configuration files are read at session start.

Since the latency of Gamescope’s FPS limiter still seems to be a problem, and we’re still doing a pretty slapdash thing of using MangoHUD’s limiter instead, I went ahead and made a script that makes it just a little cleaner.

After you save it and update your PATH variable as documented there, you can just use mangolimiter [-f FPS] %command% as the launch command.