Toward the end of the article they use chroot to run an entire rootfs as sort of a user-level system emulation.
The next step is to do the same thing except using containers/namespaces. I was able to run a Yocto rootfs build for ARM completely, including init, and IIRC networking, using LXC and binfmt_misc. A very handy technique for testing and it does run much faster than full-system emulation.
Now I found a way to get arm64 crystal binaries. I got rid of the container, but Invidious still cross compiles to amd64, so qemu is still used to run an amd64 build Invidious of transparently.
binfmt and qemu-user do wonders. It works well. One could use box64 [1] instead of qemu and it should provide better performance because it uses the native versions of some well known libraries (including libc6) instead of emulating them, but I failed to compile box64 this weekend so I stayed with qemu.