It’s not entirely clear to me which historical data you want, but in general I can say that SonarQube is focused on “now” and not architected to make a historical usage audit easy.
That said, “actively using the… instances” can be interpreted multiple ways. My CI chain can be configured to automatically analyze every commit, but if no one ever looks at the results, is that “using” it? If this is your definition of “using” then you can look at projects’ analyses histories (the project Activity page) to see analysis frequency, subject to Housekeeping.
Conversely, I might be actively browsing issues from the last analysis, but that analysis could be months old. This use is going to be harder to trace since I’m told the access logs aren’t straightforward to parse.
A third case is that I’m using SonarLint in connected mode and/or PR analysis to make sure no new issues are committed into master, without ever pointing my browser to SQ. Is that “using”? (Same comment as above about parsing the access logs).
What if SonarLint isn’t in connected mode? (Okay, nevermind. That one’s probably not “using” the SonarQube instance.)
You haven’t mentioned your underlying motivation but I feel it’s relevant mention that starting in 7.7, instance admins will be able to see the last time each user logged in (SONAR-5611).