Linux

There is probably no way to opensource it without also making it easier to bypass.

I want to highlight this in case OP missed it. Your point here is critical.

Now I'm going to nerd out a bit about it:

To expand on your points above (for OP), there's an impasse here between the anti-cheat developer and the distro developers.

The anti-cheat developer needs support from the distro developer to get their anti-cheat packages signed, to allow them to run in the kernel. Any package not signed by the distro developer that tries to run at kernel level will be treated by the OS as a virus. (Windows has this protection as well.)

Getting the code signed is pretty easy. The only requirement is sharing the source code, so the distro developers can make sure there's nothing nasty in it.

But the anti-cheat developers feel that they need to never share their source code, to prevent cheating. In some cases, they have even have contracts that prevent them from legally sharing parts of their source code (if licensed from a third party).

That's also not a problem. All they have to do is sign a binding contract for secrecy with every contributor to the distro, and then privately share their source code, and get it signed.

On Windows, that means signing a contract with Microsoft. On Mac, with Apple.

But on Linux, is just means tracking down and making separate agreements with a few thousand independent individuals...

So the technical solution is pretty simple: share code, get code signed, run in kernel.

But the contrasting needs of everyone involved make it unlikely on Linux.

Interestingly, an Anti-cheat developer who felt very confident that their code was unbeatable, could just publish it publicly, and get it signed and running quite quickly.

But uh... Most anti-cheat is also pretty low quality code, according to most estimations.