For everyone who used this guide to setup their Joplin-Server:
The Joplin team released an official Arm64 image on Docker Hub. You should definitely migrate to this image if possible instead of using the third party ones as described in their post: An official ARM64 version of Joplin Server is now available!
I updated the instructions to include the new image.
Thank you to @florider and etechonomy for your work in the past years!