Many home servers require account creation on their website, e.g. systemli.org, systemausfall.org or activism.international, and do not provide open registrations in the Element app.
To make curium cover the whole process, we could add a step to create an account on the home server's website and then proceed with the login process (#72).
Curium may offer a drop-down to choose from recommended home servers and link to their website, if required, or proceed with in-app registration.
Alternatively, curium could guide the user through the in-app registration up to the point where Element shows the warning "Registration has been disabled on this homeserver." and offer some instructions for that case ("If your homeserver has disabled registration, you may try to create an account on their website.")
Combining with #73, this would allow me to invite people to those servers and provide them with curium as a step-by-step guide.