The number of participants on Bluesky is small, and everyone seems to know each other. Getting even a single like on a post is an accomplishment, and getting 16 likes (I think) gets you onto What's Hot. Approximately nobody is interested in technical discussions; Mastodon is much better for that.
The vibe on Bluesky is weird. Everyone is very enthusiastic about being there, and most of the discussion is about being on Bluesky. Someone said that everyone is Extremely Online and much more interested in meta-discussion than discussion, and I'd agree. Bluesky is all about the in-jokes and memes, which turn over at a dizzying rate, much faster than even Twitter. It's a very horny place, with lots of butt photos.
I don't want to be negative about Bluesky. For people who want a tight-knit community to chat with, it's great. But don't feel like you're missing out if you don't have an invite code. (BTW, I don't have any to give out.)
Edit: I'm not hyping Mastodon here, just comparing Twitter alternatives. Unfortunately, so far I've found that Twitter is the best choice for me. I get maybe 10% of the interesting technical discussion on Mastodon that I get on Twitter. And I still don't understand how to work with the federation. There's also Newsmast, a new social app that reached out to me, but there's approximately 0 content there.
One thing I forgot to mention about Bluesky is that it looks exactly like Twitter, so much that I can forget which app I'm on. It's very different in that regard from Mastodon, which is like alternate-universe Twitter.