Lemmy's images are meant to be built on linux/amd64,
but they can be executed on both linux/amd64 and linux/arm64.
To do so we need to use a cross toolchain whose goal is to build from amd64 to arm64.
Namely, we need to link the lemmy_server with pq and openssl
shared libraries and a few others, and they need to be in arm64,
indeed.
The toolchain we use to cross-compile is specifically tailored for Lemmy's needs, see the image repository.