Why are songs that aren't on iTunes (Mixtapes) unplayable in playlists?

Hello RVNDYY,

Thanks for using Apple Support Communities.

I see from your picture that some of your songs are grayed out in iTunes. Are you using iTunes Match? How about Apple Music? Usually grayed out music means that your computer isn't authorized for that content, as in it was purchased from another Apple ID. Follow the steps below for help:

If songs appear to be missing

Songs containing DRM (Digital Rights Management) might not appear in iCloud, or might appear grayed out. This can occur if your computer is not authorized to play that content. Authorize your computer, then manually update iTunes Match. To find out what Apple ID your computer needs to be authorized with to play a specific song, follow the steps below:

1. Open iTunes.
2. Locate and select the song that you want to play in your iTunes library.
3. From the menu bar at the top of your computer screen, choose File > Get Info.
4. In the Summary tab, find the Account Name field in the right column. Write it down.
5. Click OK.
6. From the menu bar at the top of your computer screen, choose Store > Authorize this Computer.
7. Type in the account name from the Summary field and enter its password. Click Authorize.

Resolve issues with iTunes Match - Apple Support

Take care.