To be able to use wireguard the option CONFIG_CRYPTO_BLKCIPHER needs to be enabled.

>>> Emerging (1 of 1) net-vpn/wireguard-0.0.20190601::net-kit
 * WireGuard-0.0.20190601.tar.xz BLAKE2B SHA512 size ...                                                                                                                 [ ok ]
 * Determining the location of the kernel source code
 * Found kernel source directory:
 *     /usr/src/linux
 * Found sources for kernel version:
 *     5.16.12_p1-debian-sources
 * Checking for suitable kernel configuration options...
 *   CONFIG_CRYPTO_BLKCIPHER:     is not set when it should be.