Not sure how I got to lemmy.one but when it said I had to login to comment on something, my userid/pwd that works here didn’t work and the registration link said user registration is closed. Aren’t lemmy logins supposed to work across the whole federation? Or are there multiple federations and lemmy.one is entirely different? Maybe I misunderstand the whole scheme of lemmy.
No, this isn’t how this works. Each instance manages its own users in its own database. All that is federated is the posts and comments. You should be able to post and comment to other instances’ communities but if you want an account on another instance you have to create one.