New iPhone not recognized by IMac computer

After several hours of troubleshooting with Apple rep, my 2018 IMac desktop still will not recognize my new iPhone 8 as a new device on music app.

We finally we’re able to get albums transferred to IMac computer but it still can’t transfer my music to my IPhone 8 because the device is not recognized and does not come up on music app.

Phone beeps itself when connected but no iPhone icon appears in music app.

Rep gave me several steps to try if I like and is calling me back.

Any suggestions in meantime?