I've had a little process running for the past year or so, totting up Mastodon "active monthly users". Occasional bumps up (one outstanding one last summer when Elon did something particularly idiotic) followed by long slow declines.
Was somewhat disappointed to see recent growth of about 250k turning out to be a phantom instance (telling lies via the API).
#mastostats
There are some people out there exporting and diffing with #Diaphora binaries with more than 250k functions each.
Yes, it isn't exactly fast. But works.