My personal logic suggests that you shouldn’t be able to „save“ your iTunes library on an external drive. So, why is that? Well, first, why would you want to? Your iTunes account is linked to your Apple ID, sorry, Apple Account, and you‘ll have access to every content you’ve bought on iTunes on every device you’re signed in on, except for content removed from iTunes due to copyright, license, or other conflicts. So, if you don’t mind the last part, you should be fine. Also, let’s say you would be able to store your library on another device. It would obviously be saved as FLAC, ALAC, MP3 or a similar format, because saving it in any context to iTunes, it wouldn’t make any sense to store it there in the first place. And if you’ve got it saved in FLAC, what would stop you from making it accessible for free or selling it saved on your drives, without a license, committing copyright infringement? Right! Nothing! So, I believe that you won’t be able to store it there.
sorry if you needed it