My new Mac says I need to join Apple Music to access my library

My new Mac says I need to join Apple Music to access my library. I want to import a song I just bought to my video software but I can't even access the music app on my Mac mini. I can access on my phone so what is the problem? I've tried downloading and that doesn't work either. It says I need to subscribe to iTunes Match or join Apple Music. Can anyone help, please?