It's not about having the necessary version. The feature has to be cookie driven, right? Otherwise, mastodon.social wouldn't be able to remember that an unauthenticated visitor has an account elsewhere. Such a cookie almost certainly won't be available across servers (thanks, ad trackers for ruining it for everyone). That means a user would have to fill in that form for every single remote instance they visit.
Think of it this way: suppose a user visits a tiny Mastodon server at social.example.com. They click a user's follow button. How will social.example.com know to redirect the user to the home instance they configured when they visited mastodon.social?
> If I’ve downloaded the Mastodon app without having a server in mind what is the app supposed to do, just list them all?
If someone clicks the "pick another server" option, they're taken to a perfectly serviceable chooser. That should have been the default. It works for all the other apps that don't default to mastodon.social.
