Q: Can I add an apple music song directly to a playlist on my iMac or must I first add it to my library?

Hi Redneck in exile,

Thanks for using Apple Support Communities. Based on what you stated, it sounds like you want to add a song from Apple to a playlist. I would recommend that you read this article, it may be able to help the issue.

Add music from the Apple Music catalog to your library - Apple Support

On your Mac or PC:

 

1. In iTunes, find the song, album, or playlist that you want to add.
2. Click the More Options icon  to the right of the song or album name.
3. Click Add to Library.

Cheers,

Mario