Maybe just the circles I run in but these are not evergreen questions in my experience. I don't even know what "go back" is supposed to mean here, or for that matter what it would mean in a Windows application. Is there a system level "go back" in WinAmp/Excel/SimCity/Photoshop I've never seen before?
I was referring to IOS, not MACOS
Androids do have universal back button at the bottom on the phone or the same swipe gesture if you want but iphones do not.
Sometimes swipe (the direction and position is a guessing game), sometimes and x (right or left ) and the behavior is inconsistent too (back or close)
There are some guidelines but more often than not seems like every app has it's own method and you need to get used to it