It's a very long post, but a lot of it is a detailed discussion of terminology in the appendix -- no need to read that unless you're into definitional struggles.
Blueksy's approach to decentralization is very different from ActivityPub but it's definitely decentralized. (Also that article's over a year old, and some things have changed since then.). But, like I say in the article, not everybody is so welcoming!
They're still cosplaying decentralisation. Google hosts images on a separate domain to the one where they serve documents, are they decentralised? When we see more indexers, by all means let's consider BlueSky decentralised, but until then, they're just offloading traffic.
I hope they start supporting people who want to run an indexer. Right now they just point to their source code and say, "if you can get this largely undocumented complex service running on your own, you can run a indexer, but don't ask us for any help".
I'm not entirely confident that it will happen before their only funding source decides to cut off the cash flow.
Kuba's link i that thread is good, it looks like there's currently about 370 PDS's -- Bridgy Fed got an exception from Bluesky so is the only one that currently has more than 10 uses. https://blue.mackuba.eu/directory/pdses I know some people who just run the open-source code for Bluesky's PDS (which is pretty straightforward) and some run other implementations.