How to deauthorize all old dead computers and phones from 2023 MacBook Pro or from iPhone 12 Pro?

There is no way to deauthorize individual computers that you don't have access to. You will need to deauthorize all. Also, authorization only applies to computers, not to iPhones.

See the "Deauthorize All" instructions below 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.

iPhones are not authorized devices but can be associated and are not affected by the above. To remove associated devices, see: View and remove your devices that are associated with Apple ID purchases - Apple Support

For other information, see: Authorization vs. association - Apple Community