Going to copy paste the response I made when this was posted in a different community:

When the Twitter migration happened, a lot of folks got overenthusiastic about the idea of the fediverse and started setting up their own Mastodon instances, despite having little to no experience with selfhosting before.

A lot of such instances have since shut down as they realised the amount of efforts that actually needs into hosting such a platform, especially instances with open registrations. However, a large number of them did survive and are now thriving.

Has the growth rate slowed? Sure, just like it is expected happen after a sudden influx. But it is false to say that Mastodon growth has stalled. Instead, the phrase I would use is ‘stabilized’. Mastodon growth has stabilized into a healthy level as user growth is now happening more organically. Some stats below:

12,808,214 accounts +217,864 in the last week

Stats on most active instances:

By number of users:
https://i.postimg.cc/fb6FyY89/Screenshot-20230625-121432-Firefox.jpg

By number of posts:
https://i.postimg.cc/cCWbM0y1/Screenshot-20230625-121509-Firefox.jpg

How can anyone look at these numbers and say that the growth has stalled?