Music Mixing

With the old i-tunes I was able to build separate playlists according to genre which I would assign, ie, Classical, Jazz, Punk/New Wave, etc etc. If I wanted to mix up genres for good passive listening, I would go to the genre list, click on all the appropriate boxes with the checkmark, to play the chosen songs, go to the next genre list do the same. In other words, If I wanted to mix Springsteen, The Ramones, All of my Classic Rock, and throw in a bit of Jazz, it was easy to click boxes in each genre, then go to the (all) songs playlist and only the music that had a checked box would play. How is this done in "MUSIC"? I've attempted to build files but the contents in files disappears after not being played. Oh BTW, I'm operating 14.1 Sonoma. I've already invested a lot of time learning this new system and much of it is easier to navigate than i-tunes was. But I'm stumped with this one, as most all the advice I have read is geared toward those that want to merge with their i-phones. MY daughter asked, why not, whats the problem? My reply was two fold, I've been organizing music and photos since 2004, my collection is massive, about 400gs and I need to keep it organized and accessible. My desktop is a tool, for curating music, listening to my collection of music and for my other hobby, photography.