You can’t prevent wall hacks with only server side anti cheat. The client needs that data locally before the enemy is rendered on screen.

As mentioned in another comment, you can’t do this on the server without expensive checks for every single player that is always checking line of sight, because it’s not just your session running on a single server but multiple sessions.

And let’s say you did this, now you have a latency problem because most modern games to make them feel fluid has client side prediction with server reconciliation. This is what makes your modern games feel more responsive, if you put a constant server check there you have lost this.

No matter what people say online, it isn’t just move all of it to the server, there is data the client needs to know and can’t be spoonfed by the server.