It's been on a steady downward slide for the last year, from almost 2m during The Exodus to about 900k active users now. People sign up, but most don't stick around. I also can't help but notice my own timeline has slowed to a crawl, and it's mostly the same few people. It's not vibrant and busy like it used to be.
Aggressive growth and addictive velocity are cancerous, let it reach a healthy equilibrium. Slow can be good, too.
I'm following ~500 people at the moment, and getting relays from a few instances. I see a constant flow of new stuff but I can also easily leave and do other things, because Mastodon isn't designed to maximize engagement and addiction. I don't feel a constant need to post or comment or chase endorphins. The scale is just fine for me.
I was on there when it was just Mastodon.social. It was more vibrant then, and it's been more vibrant in recent memory, before it rocketed to 2m users and started falling. Something is different, and it's not good. I think people who've been there are getting fed up with problems no one seems to care about years on (even people like me who kept giving it chances and pushing for change), and new people are going somewhere else instead of trying Mastodon.
You can stick your head in the sand if you want and hope the year-long freefall stops rather than consider there might be a problem. It's what I've come to expect.