A quick summary of events and what to do now... to copy/paste to any confused redditor and invite them to Lemmy or kbin.
In short, Reddit is killing off most third party apps and bots, like Apollo, which provided the moderation tools that let reddit's feed not be full of spam and garbage, and are what made this site even usable on mobile. They're doing this by charging insane amounts of money that no one will be able to pay (20 million dollars for apollo). They're also straight up lying about and insulting the app devs. Here's Apollo's dev debunking those lies.
People protested. First, subs were closed and privated, but were forced open by admins, so now they're protesting by only allowing John Oliver pics, or taking sub names literally.
Alot of them them have moved to Lemmy and kbin, which are both compatible with each other.
Sub.rehab lists subreddits that have officially moved off of reddit. Honestly, just ignore the few that aren't on Lemmy or kbin. Just join the largest Lemmy or kbin community for full compatibility.
There's also Lemmynsfw.com for NSFW communities/subreddits (not listed in sub.rehab) that you can seamlessly access from any instance/server the same way explained in the picture linked above.
Just join any Lemmy or kbin server/instance to access everything; doesn't matter which because they're all connected. Lemmy.world, Lemm.ee, vlemmy.net, kbin.social, fedia.io are all great for example.
For subreddits you like that haven't moved off of reddit yet, send a polite message to the mods asking them if they plan to make the subreddit/community in Lemmy/kbin.
Copy/paste this summary anywhere relevant to spread the word.
Beware, though, that not all of them are really connected. For instance, beehaw recently defederated from lemmy.world and shitjustworks.
I would also add that yes, in general one shouldn't overthink which instance to sign up on, because you can still mostly view content from all other instances. However, you might take a few mins just to check the rules and philosophy of the instances. It's basically like assigning yourself to a Harry Potter house. In the end you'll all end up interacting in hogwarts, but being a slytherin can mean something different than being a griffindor
People will not see any posts made by lemmy.world and shitjustworks in beehaw.org communities.
Users in beehaw.org can't see posts and comments made by users from lemmy.world and shitjustworks anywhere
lemmy.world and shitjustworks users can still see posts and comments made by beehaw users
Basically, stay away from beehaw communities no matter where you are, unless you're on a beehaw account for some reason. And don't reply to beehaw users because they won't see it.
Ironically, this harms beehaw more than it harms us because people will just stay away from them. Maybe that was their goal though, to have less users...