HPKE is an implementetion of RFC-9180 Hybrid Public Key Encryption API. Depends on LibreSSL libcrypto library.

pacman -S libressl

Make sure to get LibreSSL libraries.

PKGCONFIG_DIR=/usr/lib/libressl/pkgconfig/
meson setup builddir -Dpkg_config_path=$PKGCONFIG_DIR
cd builddir
ninja test

LibreSSL's libcrypto library is not gonna be your default libcrypto library most likely. So you have to specify the directory libcrypto.pc file exist.