Wireguard is a new VPN solution included right in the Linux kernel. It’s part of the mainline kernel since version 5.6. Debian Bullseye has Linux 5.5, but the distribution maintainers decided to backport Wireguard, so it’s already available by default. Sadly, this broke the installation process that is usually suggested on the Internet.
Now, the installation is even simpler, it’s just needed to install the
wireguard-tools package without the recommended dependencies:
apt install --no-install-recommends wireguard-tools
apt installs also the
wireguard-dkms package. This package tries building the kernel module, but it fails because the code conflicts with some of the backported kernel features.