I thought wireguard is kernel-mode software and I disliked it because of that. Interesting, may be there's Linux version of user-mode wireguard. I wonder what's the performance difference between usermode and kernelmode wireguard.

There is user mode wireguard for Linux, it is wireguard-go: https://git.zx2c4.com/wireguard-go/.

There is also BoringTun: https://github.com/cloudflare/boringtun which is faster

Disclaimer: I wrote BoringTun

There is a go implementation of WireGuard with a fairly hefty warning at the top. [0]

There's also official documentation for how a userspace implementation should behave. [1]

The android version of WireGuard has a userspace implementation for devices without WireGuard in the kernel, which at the moment is pretty much all.

[0] https://github.com/WireGuard/wireguard-go

[1] https://www.wireguard.com/xplatform/