I’m glad this topic was bumped (purely by coincidence). I guess the issue has been around for a while and isn’t limited to Apple Silicon Macs.
I was having the same issue on my M1 iMac following the same guide as you. @blake was awesome and managed to find a workaround for me.
I was able to get it working on my m1 mac. I’m not exactly sure what the issue is, but this is a work around that you can use.
From the first terminal tab run:
bin/rails server --binding 127.0.0.1
From the 2nd terminal tab. Change into this directory inside the discourse directory.
cd app/assets/javascripts/discourse
Then run this command:
ember server --proxy http://127.0.0.1:3000
Then browse to http://localhost:4200