how do you purchase music in Apple Music without a subscription

No, the iTunes Store is still available on a Mac or PC.

If using iTunes on a Mac or PC, make sure the Store section is selected at the top.

If using the Music app on a Mac running Catalina, make sure you click on the Store section in the side Panel. If you can't see it, you may need to enable it. See here under "Looking for the iTunes Store": What happened to iTunes? - Apple Support

Hello Rubr,

It sounds like you are wanting to purchase music and not have an Apple Music subscription. You can purchase music from the iTunes Store, this does not require any subscription. Check out this link to learn more about purchasing music for the iTunes Store.

Add and download music from Apple Music or buy music from the iTunes Store

Cheers!

Apple Music is a subscription service you cannot purchase any music from it.

If you want to purchase music, you need to use the iTunes Store App.

This icon: