I think it's generally true that Arm is more efficient and better for the environment.
There are 3rd party Arm images available and I'm running instances with these on AWS and Oracle, but they are not updated as frequently as the official images: https://hub.docker.com/r/masquernya/lemmy/tags
I know if I'm asking I should be ready to help, and I am. But this isn't something I know how to do.
Here's an example dockerfile I wrote (for a different project) that's a little more transparent