Are most songs nowadays mixed in stereo or mono?

I'm a bit lost, but I'm not really experienced with mixing / EQing. I've seen people who recommend using mono as a reference to make a stereo mix sound even better. Are people using vsts/plugins/Midi keyboards mixing in mono or stereo or is each individual track mixed differently? Because wouldn't plugins/Vsts be one input? Im wondering how most listen to songs anyway. Like are most songs on spotify/Youtube/Billboard charts mixed in stereo? Because most people listen in headphones or radio.