Transferring music from CD to iPhone SE and iPad via external USB CD drive

You don't. You move the CD to your iTunes (Windows) or Finder (Mac) Music library on your computer, then you sync the music to your iPhone connected to your computer.

Import songs from CDs into iTunes on PC - Apple Support

Import songs from CDs into Music on Mac - Apple Support

Then Sync the music to your iPhone:

Sync music between your Mac and iPhone, iPad, or iPod touch - Apple Support

Sync iTunes content on PC with your devices - Apple Support

• Mac Book Air Retina 13"
• iPhone SE :- Does not use iCloud Library
• iPhone 6 :- uses iCloud Music Library

This is two a Step Process (To sync music from this computer, turn off Cloud Music Library)

1. Apple Music: Import music (MP3) to Apple Music Library on Mac
2. Finder: Sync between Apple Music on Mac and iPhone

Watch the GIF for the complete process

To sync music from this computer, turn off Cloud Music Library.

Watch the same GIF as a QT movie file uploaded by me on YouTube:- Transfer MP3 Music from Mac (Catalina) to iPhone (iOS13.3)

HAB21 wrote:

My iPhone is connected to the computer but there is no sidebar

What type of computer? Windows or Mac? If Windows, have you downloaded the latest version of iTunes? Assuming you have Windows 11, iTunes should be downloaded from the Microsoft Store.

I read the links and didn't see where a subscription to Apple Music is required. Contact Apple Support for direct help. If you're in the US, you can call Apple at: 800-MY-APPLE