Or possibly the number of downloads of the setup.exe file?
Maybe statistics too. From the Legion forum.
In general it is pretty much impossible to track absolute downloads. There have been mirrors of the MusicBrainz file servers, many third-party download pages offer Picard, Linux users usually install not by download but from package repositories etc.
I mentioned some data from the Microsoft and Snap stores in my talk about Picard on this years MetaBrainz Summit, see the slide at State of MusicBrainz Picard 2023 - Google Slides
On the actual talk some people also added additional comments. Rob estimated the overall download numbers over the entire time to go into the 10th of millions. See also the end of the talk at
@zas actually had had a look at request statistics of MusicBrainz and how many requests are originating from Picard. I don’t remember the numbers (might be it is recorded in the discussion of the talk above), but it is I think the most indicative data on how many active Picard users there might be. It also showed the distribution of operating systems, with by far the most Picard users using Windows, followed by Linux and then macOS.