If some player is stubborn and doesn't resign use horse riders to scout everything, preferably with custom-walk (hold alt and hold left click to draw a line) so the riders walk parallel to scout a lot of area. If that doesn't work light up the whole map with outposts and have a look on the mini-map for the color. That should do the trick. If not double check the victory condition.

Updated : Significant performance improvement (First version was bad, this one fix it but also improve wall placement performance impacts in general)   Now other towers can be used as a starting or end point for wall placement instead of wall towers. This doesn't prevent you from walling easily around them : you can also snap walls and palisades to their edges! (The threshold distance makes it so easy to choose between the two you won't even be bothered).

If they're still remaining you haven't won yet; did you capture or destroy the big central building (CC)? Sometimes there's just a civilian standing where they last worked, sometimes all remaining units run somewhere to build a port.

By default, the win condition is "conquest". Take out all hostile units and buildings. Any more questions?

newb here I've built a huge army and stamped out basically the entirety of the bot and there's just bits of houses and stuff remaining. What do I do so I can finally win?

So funny I can put a label in my name depending on the state I am in

You might take a look on Issue #3177 ([PATCH] Implement camouflaging) over there at Wildfire Games' Gitea instance.