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.
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