I only have 1 device authorized, but when I try to authorize another I get a pop up warning that I have 5 already authorized.

Try Deauthorize All and then authorize the computers that you still have and want to use (computers only, not iPhones or iPads). See the following from Authorize or deauthorize your computer for iTunes Store purchases - Apple Support

To deauthorize a computer that you don't have access to, you have to deauthorize all of your computers. Then authorize each computer that you have again. You can deauthorize all computers only once a year.

1. Open the Apple Music app or Apple TV app.
2. Choose Account > Account Settings.
3. Sign in with your Apple ID and password. Forgot your Apple ID?
4. At the top of your Account Information page, go to the Apple ID Summary section.
5. Next to Computer Authorizations, click Deauthorize All.
6. Authorize each computer that you use again.