A lot of estimates... but estimations don't give the prevalence.
One number that I believe:
Chess.com has surpassed 20,000,000 members
There are other websites with chess players, but the numbers are not cumulative as a player could register to several websites.
The FIDE has 360.000 members.
In USA, around 90000 players are part of the U.S. Chess Federation.
Finally, among all the players in the world, around 1600 were crowned Grand Masters...
A good reference:
https://www.chesshistory.com/winter/ext ... ayers.html
If you have some ideas or some answers, please feel free to post here...
kr,
Maurice