On the same browser, in the same instance, you're only going to be able to log into one at a time on that browser. An account may show up if you search for it, but you would have to log out and log into the other one to use it. But, when the instances are different, you have no issues at all switching between them. It's like being logged into amazon and eBay at the same time on a browser

Afaik, there's nothing saying you can't have accounts all over the place, in multiples, as long as the owner/s of the instance don't have a rule otherwise.

But! I would start with one account in one instance for a little while until you get used to the fediverse and navigating it. Less to keep track of.

And you don't need multiple accounts on multiple instances to use lemmy. That's the point of federation. They all can talk to each other, so long as a specific instance isn't defederated. There's a few that are almost totally defederated because of the content on them, as an example. Those, you'd need a separate account for. But unless you're into the batshit crazy end of communism, or loli art, you aren't missing anything in those.

You can access all posts from (most) any instance. For example, you are currently posting to a lemmy.world community and I'm replying to you from lemmy.world, but you are browsing from sh.itjust.works. This is fine and how it is expected to work.

So, there isn't much reason to have multiple accounts, but it also doesn't hurt to have multiple.

You only need one account to navigate across the entire Lemmy instances, despite the server you choose. You can suscribe to communities searching in the glass button with pattern communityname@serverofthatcommunity.example

Real example Salsa community

You don't need it necessarily but noone is going to stop you, you can have one account for normal stuff and one for porn, just as a example.

And people saying its bad are idiots...

Hello there, and welcome to our community! I hope you like it in here.

Could you paraphrase your title to be a question? It’s our first rule. Thank you :)

you can stick with your instance and view across the fediverse (mostly) fine!

You don't need multiple accounts.

You can access the whole lemmyverse with just one account, on one instance.