Beehaw is currently defederated from lemmy.world (https://beehaw.org/instances scroll down and look at blocked instances). While that is the case, I don't think you can sub to lemmy.world communities with a beehaw account
Not sure if this was clear from context, but you can make a new account on another instance (like LW) and use it to access content there. If you use a mobile app for Lemmy, they often have easy account switchers so you can flip back and forth easily.