For platform-independent info about wireguard, see network admin docs for Wireguard.
Enable RPM Fusion
see also: Wireguard in the Debian wiki.
After apt upgrade and apt install wireguard, reboot into the newest kernel you installed.
install Linux Kernel headers:
apt install linux-headers-amd64
let DKMS run its course:
dpkg-reconfigure wireguard-dkms