Foobar2000 with an iPod add-on[1] and a podcast add-on[2]. You don't need iTunes directly, but probably an older version of iTunes in the background for compatibility when syncing. Oldapps.com has you sorted for that.

I personally use a modded 5.5 gen for daily listening, it's vastly superior to using a smartphone. It has a huge memory and unbeatable battery life. With cheap replaceable batteries and SD card boards, it should essentially last for years/decades. The firmware is much simpler than iOS, so it doesn't matter that it's not maintained, it simply works.

EDIT: OP is using a Mac, so I'm not sure if this is feasible. It does work well on Windows though.

[1] https://www.foobar2000.org/components/view/foo_dop

[2] https://www.foobar2000.org/components/view/foo_podcatcher

Replace the firmware with RockBox and it presents itself as a normal USB storage device. Just drag and drop the files.

Syncing music still works fine on Macs/Windows. I'd actually go as far as to say that on Mac it's an improvement, becasue you just have a 'Music' app and a 'Podcast' app, and when you plug in an iPod you can see it in Finder.

It's perhaps more like elements of it seemed to be integrated into Finder so it'll mount as a device and you'll see the familiar iTunes style sync UI