Her big true crime project, "The System," shot to the top of Spotify's "Top Podcasts" list this week -- surging past "The Joe Rogan Experience" and even the famed "Call Her Daddy" ... which fell in line behind her at #2 and #3, respectively.

Meghan Markle's podcast, "Archetypes," was #4 -- and from there you got "Huberman Lab," "Crime Junkie," "The Try Pod" and "On Purpose with Jay Shetty" ... in that order.

It's pretty impressive, considering this is less than a week old. If you're unfamiliar -- this first season of "The System" tackles a case pertaining to convicted murderer Kevin Keith ... whom Kim believes is innocent, only to dive deep into the deets/evidence.

Clearly there's interest in what she has to say in a podcast setting, but keep in mind -- this is a Spotify exclusive ... so it's hard to tell how "The System" would translate across other platforms. Rogan and Markle's podcasts are also exclusive to them -- so jury's out there too.

In any case ... she's all in on promoting it. Looks like KK snapped up some old-fashioned billboard advertising in Calabasas to plug the podcast, with her face front and center.