Yes, there are alternatives such as Fraps for Mac or other FPS tracking apps designed for macOS.
Yes, there are alternatives such as Fraps for Mac or other FPS tracking apps designed for macOS.
I also discovered an app named "Count It" via a quick search. It appears to support gaming and performs reasonably well.
When the game isn't available on Steam, consider adding it as a non-Steam title. That's exactly what I did for Half-Life 3.
Yes, including non-Steam games would let the Steam FPS counter function for those titles as well.