iPod Classic - Big Sur - iTunes editing on iPod

I think this thing will be the solution to your problems. DISCLAIMER: I am NOT involved with its development; I'm just an iPod Classic fan who was frustrated with how the older iPods have been treated since Catalina (and why I didn't upgrade my MBP from Mojave until I discovered this app last week):

[Link Edited by Moderator]

The Music app and Finder in Big Sur provide reduced support for manually managed devices when compared to iTunes. I would recommend you bring all of your content into your computer, organize it there, then sync what you want to your device. See Recover media from an iPod - Apple Community.

tt2

I haven't done anything, I'm a fellow user like you. Keeping the only copy of your content on a device that could easily be lost, stolen, damaged, or experience either hardware or software failure is unwise. All your content should be in a computer based library which you keep backed up. Whether you then manually drag and drop content to a device or sync with selected playlists is up to you, but syncing provides more control and sets up an easy path to get back to where you were should a device need to be restored or replaced. The link I posted previously should help you recover all of the media from your device.

tt2

And I see the link was removed by a moderator because it was deemed "[not] directly related to the original poster's question" -- YES, IT WAS. The link was to an app called Retroactive, which allows you to install iTunes, Aperture, and other apps on the operating systems that no longer allow you to use them. That will help manage your iPod the way you always did before. Google it. It's on a Github address.