how many people are actually playing marathon on steam?

steam charts only see steam though. it's on console too with crossplay, so that number is one slice of the playerbase, not the total. fine for spotting a trend, just don't read it as the whole population.

steamdb has the concurrent player chart for it, that's the number to watch rather than reviews. look at the 24h peak and whether it's sliding week on week, not the launch figure. queue times in your own region matter more than the global count though. late at night in a smaller region it can feel emptier than the chart suggests.