Missing/Could not find "Gameplay" tab in Settings

I was puzzled by that, too. I was seeing images of a gameplay tab between 'controls' and 'interface' posted online, but that wasn't present when I went into settings. Turns out, you can only get that tab on settings when you go to settings FROM the game itself. So, be mid-play and then hit 'ESC'. And there you'll have it, all the specific combat changes and wayfinding settings. Note, it won't change combat for currently loaded mobs, so if you want to change it for difficulty reasons, you'll need to go back to a slightly older save.