At the main Stats page: https://www.inaturalist.org/stats (accessible in the website header under “More”), the total number of users is currently around 2.25 million.
My understanding is that figure includes accounts that have been flagged as spam. The total number of users on the Year on iNaturalist 2019 (https://www.inaturalist.org/stats/2019) is less than half that, at around 1 million users:
Can you exclude spam-flagged accounts from the main stats page too?