We now offer an official ARM64 version of Joplin Server as of version 3.3.13. Got a Raspberry Pi or similar? Give it a try and let me know how it works!
https://hub.docker.com/r/joplin/server/tags
Additionally please note that I will also ask for existing non-official ARM64 Joplin Server images to be removed from Docker Hub and other places. The issue with these images is that, unlike the apps, they are not signed so we have no way to know whether it is safe to run them or not. There's also a lack of transparency for some of them since they don't even link to a GitHub repository.
So if you are running one of these non-official images, be aware that you may not receive updates for them in the future, so consider switching to the official image.