Thanks for your interest and replies and sorry it took so long to get back to you.
I thought I would give you an update for your information re syncing iPod Classic to iMac running OS Catalina. I've spent a lot of time with a senior Apple engineer trying to resolve the problem. It appears the latest version of OS Catalina is not compatible with iPod Classics and that is why the music player will not sync.
The resolution is to go back to a previous OS. You can either replace your current OS with this downgrade or set up a separate volume on your hard drive (internal or external) and download a previous OS.
I created a new volume and downloaded High Sierra and then exported my tracks from Music and imported them into iTunes on High Sierra. Now I can sync seamlessly.