I believe de_dust2 is likely still the most played FPS map. Not sure which other map could have dethroned it. It can’t be Fortnite since Fortnite changes the map every few months and nowadays makes a new one every year or so.
I guess Blood Gulch from the time when Halo was super popular was a very popular map as well.
Then you also have 2fort from the Team Fortress games.
But yes I would say de_dust2 is very likely still the most played FPS map and it will likely stay that way.