Hey, I use a DAW called studio one and I literally just blend the songs together at a point near the end that sounds decent. ( over lap the songs and fade the end and start of both songs ) Start by getting a list of the songs you want in your playlist- you don’t have to mix the songs a lot of other Yt’ers don’t You can just add the list of songs into a video editing app. (Like Canva or Capcut) Hope this helps ❤