Lemmy Easy Deploy has ARM64 support.

After you got lemmy up and running on your raspberry pi, the next hurdle is making it accessible from the internet so other lemmy instances can federate with your instance. There are several way to do that, such as routing getting a static ip address from your ISP and forwarding port 80 and 443 to your pi from your router config, using clodflare tunnel, etc.

Just ask the selfhost community if you hit a roadblock. They love getting more people to join their rank.