Where is "Recent/Open Apps" Button On Galaxy J3?

if this is the correct model of the phone:
https://www.gsmarena.com/samsung_galaxy_j3_(2016)-7760.php

then it is on the very bottom left of the home button. it is the one that looks like a bunch of folders. it is not part of the screen.

edit: same goes for the 2018 version:
https://www.gsmarena.com/samsung_galaxy_j3_(2018)-pictures-8928.php

 

Of course unless there is fault in the app it will go to sleep after its finished its task and won't be using battery. And the system will clear the RAM if it needs it, whereas if you open the app again after closing it it will use more power loading it than if you never closed it and it was still in RAM.

So I'm not convinced that it's worth doing this. I never do, I just let the system manage these things.