From what i’ve read, players can modify their client in any way they want and there isn’t much that can be done about it. Wall hacking is prevalent in shooters because it’s easy to modify the client to be able to see through walls. Supposedly, someone could connect to your multiplayer game without a client!
If you can head shot someone in one click, then seeing through a wall is a big advantage and cheaters are more likely to build and use cheats at risk of getting caught.
But if you’re building a game where gun battles have to last at least a few seconds and no one dies instantly, then suddenly knowing that someone is about to come around a wall isn’t that big of an advantage and people are less likely to cheat. Less likely.
So while you can keep things like HP and AMMO accurate on the server, players can still mess with anything that they have access to on their client. Being able to zoom out and see the whole map could give a cheater an advantage if it’s “gameplay important”. Maybe seeing other things on the map isn’t important, in which cheaters wouldn’t bother. Or maybe it is important, and you could write some code to try and keep that information from being sent out to clients unless they are within range or outside of the fog of war.