On the new M1 Pro/Max and the older M1 Apple silicon chips, there really is no good way to check your FPS currently.
The steam overlay doesn't work, and I'm not aware of another convenient way to check FPS on Mac that is a realistic ask for most people. We need to know how well the game is performing when we're tweaking the settings to find the ideal settings, but right now we can't. A built-in benchmark might be too much work, but a built-in optional FPS Counter seems like a huge quality of life feature that wouldn't be too time-consuming to add.
