It should be noted somewhere on the login screen, maybe with an asterisk, that beehaw.org is not fully federated, restricted, however it needs to be termed.
Since account creation does not happen in the app, but requires visiting the instance's home page, where registration requirements, federation status and other peculiarities are plainly visible, I don't think this belongs in the app.
Yeah. I feel like a lot of instances must have at least one other instance blocked. A tech focused instance for example might not want to federate with a political alt right instance. An asterisk wouldn't mean much