It doesn't seem to be the same situation with tor exit nodes, where your node is automatically on the system. Here, it looks like people have to actively use your proxy; it tells people who run a proxy to share a URL with their friends.
And that brings the difficulty of letting your proxy be known to legitimate interested people if your iranian social presence is non-existent. I ran a Tor node (not an exit one) in Germany back in the days (it was to help iranian people).
Probably helpful context: [Help people in Iran reconnect to Signal – a request to our community] https://signal.org/blog/run-a-proxy/