I believe I read a while ago that beehaw defederated from lemmy.world. I'm new to the fediverse, so I'm still trying to understand exactly what that means. Is it still possible to subscribe to a lemmy.world community from my beehaw account? There are a couple of iOS Lemmy apps that have their official community on lemmy.world, and I'd really like to be able to subscribe to them.
No, you will have to create a separate account on Lemmy.world or another instance which still federates with them to do that. It is worth noting that the defederation is indefinite but not permanent so you could also just wait. The defederation was done because Lemmy.world users were creating an overabundance of moderation issues so the intention is to eventually federate with them again when it is possible to address those issues more efficiently.
Basically you can only view content from instances your home instance (in this case Beehaw) federates with.
Unfortunately, a few weeks ago, Beehaw had to defederate from Lemmy.world and Shitjustworks due to a lack of moderation tools.
This means you will not be able to view any Lemmy.world content with your Beehaw account until Beehaw refederates.
You may still see old content from Lemmy.world from before the defederation, but no new content will show up.
My personal recommendation if you want to see Lemmy.world content would be to use the Lift-off app for Lemmy; which can combine multiple accounts' feeds into a single feed. Then you can use a Lemmy.world account to view their content and your Beehaw account to view their content at the same time.
Lemmy.world and sh.itjust.works tried to grow their userbases as fast as possible, so they let free account creation without any screening and minimal moderation. That attracted a lot of people, but also a lot of bad actors, who then went on to use federation to cause trouble on other instances, particularly the ones they felt federation allowed them to "sneak into", bypassing whatever rules.
Beehaw's "rules" are more of an ideology than a strict set of rules, which needs more work from mods to apply. At the time it didn't have (likely still doesn't have) the mod staff needed to deal with that onslaught, so the only mod tool left, was to cut off those instances entirely. At least until they are willing to, and capable of, putting some order among their users.
Lemmy doesn't even have a way of reporting users to their source instance (a feature that would pose its own set of challenges), so they can pass as model citizens on their home instance, while wreaking havok everywhere else.