I’ve run into a similar problem, connected my iPod 7th gen to my MacBook Pro to upload more music, only something happened to corrupt the music files I already had on it and my MacBook didn’t register the iPod. The iPod was fine, but it didn’t recognise the music files, but the hard drive had them on there, but not as music files. Did a hard reset, then reconnected, but the MacBook only recognised it as an external drive. Used Clean My Mac to repair the iPod hard drive, which sort of worked. I wiped the hard drive, it’s like new, my MacBook recognised it, but couldn’t connect. Said it needed to download the recovery software. Only Apple don’t have it anymore for my MacBook to download. Just had a very long, but unproductive hour long chat with Apple Support, who kept telling me to do everything I’d already tried then he (didn’t give me his name, suspect it was an Indian call centre) just gave up and told me to book it in for a repair, even though it’s a software issue. Really disappointed by this, last time I had a problem like this, they did a remote access on my MacBook and sorted it out.