Was just over at the Reaper forum, I don't know if the user number is anything to go by, but it gives an idea:
Curious ... I don't see the viewing numbers.
Numbers of threads and posts differ more, but then Reaper for Linux is much more recent than Win & Mac versions.
Similar thread/post ratios on Mixbus forum; Ardour has more Linux than the others as one might expect.
There are almost certainly more people interested in and/or using Linux than people tend to think. Of my circle, most just use tablets, but of those that use PCs around 1/4 use Linux at least some of the time. I may have been partly responsible for that, though, so my circle may have a skew.