login to lemmy.world travel to lemmy.ml and be able to comment.
See, this is kind of impossible because of security reasons.
Imagine logging in on gmail, going to facebook (without any further action in between) and being able to read your emails. That would be convenient but catastrophic!
Yes, I know, FB and gmail are two different things, but the concept of auth is the same. A website saves a cookie in your browser and uses it to check whether you're authenticated or not. And that website can AND SHOULD only be able to read its own cookies.
Why don't they just rename it to "AdOS" already?