No.
My very limited understanding is that you can have different accounts on different instances, with the same name.
E.g. sicjoke@lemmy.world and sicjoke@lemmy.social
Much like you can have different email accounts on different email platforms, with the same name.
E.g sicjoke@gmail.com and sicjoke@hotmail.com
Anyone feel free to tell me I am talking bollocks.
No, each instance has it's own accounts. You can use an account on any instance to subscribe and comment on communities on any other instances though.
There is an exception with defederated instances, but if you're not trying to start a communist or nazi revolution you probably won't notice.
Oh except for couple instances that had to defederate because there's so many new people and the load got too much for a few. I think that's all sorted out now.
What do you mean by "same account"? Do you mean "same account name"?
If you want the same account name, you can register for the same account name in a different instance—assuming of course, that no one in that other instance has already registered under that username.