In short, Reddit is killing off most third party apps and bots, like Apollo, which 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.
Picture to explain simply how Lemmy and kbin work and how they're compatible; they are both part of the Fediverse.
Sub.rehab lists subreddits that have officially moved to other platforms, but honestly, just ignore those not 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, kbin.social, fedia.io are all great for example.
You should mention the Beehaw thing in your post. It's one of the bigger instances and someone could join not realising it's defederated.
Beehaw is already doing some weird moderation to protect their agenda. I'd avoid them like the plague.