WSL2 still runs in a VM so it has the performance implications of that, not that they usually end up being that significant (I have found that memory usage in WSL2 is usually ridiculously high, though).

I think the support for Linux GUI applications is achieved by running an X server on the Windows side of things.

WSL2 uses a Hyper-V virtual machine [1], which is a native hypervisor [2] and doesn't come with most of the performance costs of software VMs.

[1] https://en.wikipedia.org/wiki/Hyper-V

[2] https://en.wikipedia.org/wiki/Hypervisor#Classification

Funny thing is that most of my stuff runs faster in WSL2 than Windows because it bypasses Windows built-in virus scanner.