Apple Music does not display my Library on iTunes

iTunes is no longer available on the newer MacOS. You must use the Music app instead. (You do not need to subscribe to Apple Music.)

See the 'macOS 10.15 Catalina and later' section in:

Move your iTunes library to a new computer - Apple Community

The library is probably still on you Mac, just in a different location.

I can't access my Itunes library. I have a pretty heavy investment in something I can't listen to.

You can only see / play your music on your phone if EITHER the music is also in iCloud, OR you have set up your music to be sync'd from your Mac directly to your phone (like the old iPod days).

I have an iPod Nano 6th Generation on which I would like to put some Podcasts. How can I do this please?