Hi Rawer88,
Thanks for reaching out to Apple Support Communities.
It sounds like you're having an issue with syncing your iPod nano to your Mac.
We're happy to assist.
We recommend checking out the steps in the section titled "Sync or remove content using the Finder" from the article here: Use the Finder to sync your iPhone, iPad, or iPod with your computer
1) Open a Finder window and connect your device to your computer using a USB cable. Learn what to do if you don't see your device listed in Finder.
2) After your device appears in the sidebar of the Finder window, click the device to select it.
3) If prompted, trust your device. You might be asked to update to the latest version of iOS or iPadOS.
4) Select the type of content that you want to sync or remove from the horizontal list. To turn syncing on for a content type, select the checkbox next to “Sync [content] onto [user’s] iPhone.” More syncing options will now be available.
5) Select the checkbox next to each item that you want to sync.

6) Click the Apply button in the lower-right corner of the window. If syncing doesn't start automatically, click the Sync button. You may also be prompted to authorize your computer to complete the sync.
The reason why we’re recommending the steps above is because they directly address the issue you initially posted about: you're having difficulty syncing your iPod nano to your Mac.
Please do not hesitate to reach back out to us if you have questions or need any additional support.
Cheers!