This is a kernel module for FreeBSD to support WireGuard. It is being developed here before its eventual submission to FreeBSD 13.1 or 14.
First make sure you have the latest net/wireguard package installed, version ≥1.0.20210315.
Then, on FreeBSD 12 & 13:
# git clone https://git.zx2c4.com/wireguard-freebsd
# make -C wireguard-freebsd/src
# make -C wireguard-freebsd/src load install
After that, it should be possible to use wg(8) and wg-quick(8) like usual, but with the faster kernel implementation.