a user gets sent a link to a thread in some remote fediverse site.. which the browser dutifully opens. but then the user cant comment, because they are not logged in. user is confused. it is a common user story.
for some people this is obvious, for others its a problem. google/facebook kinda get around this kind of thing with an SSO process (login with google!)
at its root is the problem of finding remote communities for which one would want to subscribe.
what you Really do, is take the community/magazine/thread and subscribe to it over in your own instance, which will then allow you to comment in your local instance.