Here’s some more of the owl, the official docs: https://element-hq.github.io/synapse/latest/usage/configuration/config_documentation.html#registration_shared_secret

So add this to your matrix config:

registration_shared_secret:

I’m guessing this string can be whatever you want it to be.

But yeah, I agree in general, some of the docs can be pretty opaque. For example, I wanted to configure NextCloud w/ Collabora in Docker, and I kept getting errors when trying to do what a few sites recommended. I ended up figuring it out, but only through trial and error. I’m going to go through the same pain this weekend when I try out ownCloud Infinite Scale up and running to compare.