I did the math not too long ago, basing it on the best and most recent numbers I could find. There are somewhere between 38,000,000 and 44,000,000 desktop Linux users.
I was unable to find the numbers for server installs, but it probably dwarfs that number when you count virtual servers - as many hardware servers will have many virtualized OSes on it. One server may have hundreds of virtual instances running on it in the form of a VPS or similar.
For some scale, all the top 500 supercomputers run Linux (last time I checked).
In 2016, RackSpace (RackSolutions) determined that there were ~100,000,000 servers across the globe and that they'd need 4x that amount to handle the web by 2020. Statista seems to indicate a giant upswing in server purchases, but the complete stats are behind a paywall.
Each of those servers may have multiple sites and multiple instances of Linux running on them. Those numbers seem to only include those servers that aren't dark - meaning they're public facing. So, that's not business' private servers (probably).
Exact figures are hard to come by, at least with my search terms.