macOS gives each user a ~/Music folder into which data from music related apps can go, e.g. iTunes, GarageBand, Logic, and now Music (the app). Music (the app) normally puts its library at ~/Music/Music. Inside that it places a media folder, called Media, or internally Media.localized. Prior to iTunes 9 iTunes would put artist folders inside the media folder (then called iTunes Music) which also held the special folders for other media types such as Movies, Podcasts, Audiobooks, etc. With iTunes 9 the default media folder name became iTunes Media with artist folders being moved down into a new Music subfolder. Despite the fact that Music (the app) is now focused (almost) solely on music this extra folder is still generated by default. E.g. typically you might see ~/Music/Music/Media/Music before you get to an artist folder. The last Music folder can be removed by changing the preference file I talk about in the Managing your Mac media libraries - Apple Community user tip.
The actual location and name of your primary Music library folder are up to you, and it is also possible to use a different name for the media folder within it, or have that located elsewhere, but that all adds potential complications down the line should you want to move the library to a bigger drive or a new computer, so I'd generally recommend sticking to the standard layout if you can. When you've migrated from iTunes to Music your content may well be in the old iTunes Media folder, which could in turn have another Music subfolder, in which case the user tip has advice on manipulating the library into the new layout if you wish.
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