We're mostly talking about FPS here, you've got 2 main cheat categories: aimbots and esps (visibility hacks)
Esps are purely client side, they read actors from game's memory and draw a client side overlay. It's impossible to protect against these on the server. Even if you had perfect culling from the server (didn't send players behind walls for example) you'd still have semitransparent surfaces like foliage and smoke. There are people making good money in PUBG just making enemy textures that are easier to see. You need kernel anticheat to prevent the cheat reading the memory. Also you want to take screenshots periodically and detect overlays.
Aimbots in the olden days could be detected on the server because their movements were instant, precise, unnatural snaps. But these days cheat developers have wisened up. Again the best protection is to prevent the cheat from reading the games memory in the first place, some anticheats go as far as to try to prevent input from any artificial device (so the cheat can't create mouse movement)
There are also movement hacks, but I don't think that these are really common these days. You can detect protect against these on the server side
Just adding that occlusion only works with games that have simple geometry, 90 degree corners, straight corridors, enclosed areas and no large difference in elevation. So its useful in games like CS or Valorant, but will not work well in open games like Battlefield or Escape from Tarkov.
There's also DMA based cheats that will read memory with another computer which can then output an ESP overlay to a HDMI or DP merge box that will show both the game and overlay on your monitor. They can also do aimbot by adding mouse inputs to a device you connect your mouse.
Websites sell DMA cards and these other devices together.
Esps are purely client side, they read actors from game's memory and draw a client side overlay. It's impossible to protect against these on the server. Even if you had perfect culling from the server (didn't send players behind walls for example) you'd still have semitransparent surfaces like foliage and smoke. There are people making good money in PUBG just making enemy textures that are easier to see. You need kernel anticheat to prevent the cheat reading the memory. Also you want to take screenshots periodically and detect overlays.
Aimbots in the olden days could be detected on the server because their movements were instant, precise, unnatural snaps. But these days cheat developers have wisened up. Again the best protection is to prevent the cheat from reading the games memory in the first place, some anticheats go as far as to try to prevent input from any artificial device (so the cheat can't create mouse movement)
There are also movement hacks, but I don't think that these are really common these days. You can detect protect against these on the server side