The documentation for WaitForFixedUpdate states “Waits until next fixed frame rate update function.”.
I don’t understand what is a “framerate update function” is.
Does it refer to the same frequency as “void Update()”?
If not, what YieldInstruction should I use to ensure that each call (in a loop) is Time.deltaTime seconds apart?
Thanks in advance! 
if you want it to happen on update, just use “yield return null” you dont want to yield on fixed update unless you are doing physics stuff
FixedUpdate is where physics processing is done, and you use scripts inside that. Update is done every frame of the game. You can set FixedUpdate manually at Edit > Project Settings > Time. However I’ve never had to change these values by much. I usually lower it to about 15 steps per second if I’m having performance issues, but for most projects don’t mess with it.