It is actually still supported directly Finder on macOS. Or, even better, just putting Rockbox on them and copying files over directly, and that’s well supported in Linux.
Pricing on the used market is maybe a bit high compared to some of the other options out there but the hardware still feels great and there’s massive aftermarket support so there are still benefits to an iPod.
To be honest I like the classic UI and would not want to use Rockbox… I have struggled trying to use it with Linux. There are ways, in theory, but actually was a pain in practice. I’ve been told Finder works fine, if that’s the case then that’s great.