Why won't my iPod connect to Mac after macOS Sequoia update?

For what it's worth - and I recognize this isn't viable for everyone - I found a foolproof workaround and have tested it on a handful of iPods: An older Mac.

At this point in time, you can get an 11" MacBook Air or 2014 or older Mac Mini for under $100 pretty easily, and apart from being potentially limited in internal storage, any machine like that - basically running older Mac OS of Catalina or earlier - will reliably maintain any iPod and iTunes Library. They run "actual iTunes" and essentially work entirely as originally designed. They won't work with newer iPhone, as far as I can tell, but my High Sierra Mac Mini connects smoothly with any iPod I can throw at it.

This is kind of a classic tech conundrum and you'll see a lot of greybeard IT guys and various kinds of organizations do it this way: keep on hand one or two machines of certain vintages to perform maintenance tasks on other devices that have been dropped by newer OSes or other software. I also keep Windows 10 and Windows XP laptops on a shelf for the blue moons when those are needed for something like decrypting an old CD. The older Macs can open things like Aperture libraries and even recover files from old versions of iMovie.