I know this is sometimes impossible and/or too costly to implement but it should be possible to find a compromise that prevents most of the blatant cheaters, eventually.
Also helpers like: In any score event, for randomly selected players, analyze the last actions taken.
You just cannot trust the clients. People will find creative ways of reading the memory of their own hardware, whatever you do.
Either full of edges cases (how do you efficiently compute visibility, and can you prevent models from popping in as a result of latency) or computationally expensive[0]. Valorant, CSGO, League of Legends, Dota 2 are some of the games that I know about that implement server-side occluding to minimise the impact of wallhacks, but eventually a client will still need information like the position of an audio cue such as footsteps that cheats can make use of.
[0]: https://technology.riotgames.com/news/demolishing-wallhacks-...
Can you do that well enough on the client? The client can add some prediction on where someone is moving, but so can the server. And enemies killing you due to lag is happening already with current architectures.