Games

Modern cheats for multiplayer games don't modify local files (or attribute values in memory), since the server validates everything anyway. They're about giving you information that's available but not shown in the game (like see-through walls, or exact skill ranges), or manipulate input (dodge enemy damage, easy combos). Those cheat can run in kernel mode (or at least evade detection from user mode), so the anti-cheat needs kernel mode to be more effective.

And then a game gets updated so the hashes don't match and uh oh, everything is fucked. Oh, but we can change the hashes of the files in the executable! Yeah, so can they. People modding shit into the executable is basically a given. Let alone the fact that you'd need to sit through a steam "validation of files" length of time every time you'd need to launch a game (because validation works exactly as you have described).

What is gained is that it has access to more information. Some cheats use an entirely different program / process that reads memory and outputs info that is available to the game but hidden from the player. Like a client needs to know where a person on the other team is to be able to draw their model. So you read that, you put a little box over where they are, and bang you have wallhacks.

They can prevent you from running cheats that other anti-cheats can't detect. For instance, they could modify the value in memory so that your calculated hash always succeeds even when it's modified. This doesn't stop cheating though; it just means cheaters have to use cheat hardware that exists at a layer that even kernel anti-cheat can't detect.

For me anything important is done in the browser (very rarely) and mostly on the phone.

They will be gone with time, but not because anything that Valve does. Microsoft is locking down the kernel after the CrowdStrike debacle. In a few years it will be impossible to run any custom kernel code.

Eli5: your PC has different access levels a program can run at. This prevents a malicious or badly coded program from completely fucking your computer. Kernel level anti cheat runs at the lowest level access that exists under windows. It can do basically whatever it wants to your PC, and if a backdoor is coded in (happens way more than you'd think), it gives malware basically total access to your PC.

Try this one.

That does not detect things like wall hack and aim-bots that don't modify the game state directly.