Hello uteller3786,
Welcome to Apple Support Communities! I see that you've recently rediscovered your iPod nano (4th generation), however you're encountering an issue syncing new music to it from iTunes on your Mac. I would be happy to provide some steps to help you enjoy new music on your iPod.
Following the "Add items to your device manually" section in the resource below, see if you can select a specific song, playlist, or album to manually sync to the iPod:
Sync iTunes content on Mac with your devices - Apple Support
If this isn't the same computer that you originally synced the music to the iPod with, you may see a prompt indicating the iPod cannot be synced with more than one iTunes library. Selecting 'Yes' in the pop-up window will erase any songs and other audio files currently on the iPod, then replace it with the content that's currently in iTunes on the computer that you're using.
If you're still unable to sync new music to the iPod, you may want to consider checking for software updates, then restoring the iPod nano. This would erase any data currently on the iPod and restore it back to factory settings. You'll find the steps to update and restore your specific iPod model on page 69 of the User Guide below:
iPod nano User Guide
Keep us posted on the results.
Cheers!
