Now with this music app comes a different format of library file that is not backward compatible. So I probably either maintain the library on Mac or Windows, but no longer on both devices.
Yeah, that's gonna complicate it for sure, and typical when depending on someones Library format. Ask the question, how many times have music, photo and other Apple Library formats changed over the years, loads probably.
Give some thought to abandoning the Library formats. Maintain a music volume on an external manually, way less headaches, and you can structure it the way you wanna in the file system rather than having iTunes destroy everything, seen it way too many times.
Use 3rd party tagging tools to add the metadata if it's missing, or in the Finder get info on AIFF's, AAC's, MP3's etc and drop album artwork to them if that's what you need. Most of the time I like to name the file name, artist-track number-track title, and Folder names, Artist-Album-Disc#, it's way easier to sort folders and play tracks in order.
Doing things this way gives you the flexibility and the freedom of portability without being interfered with by software libraries.
You can use Phonix
https://phonix.nl.eu.org on the Mac to play tunes, it can list your entire music folder in a sidebar so then it's no dependent on a Library format, and just use iTunes on Winblowz to manually add tunes to your phones, or the Finder and Music on Monterey.
I've played with Music on Monterey, from what I've seen it's not really a feature finished app neither is the embedded iTunes into the Finder. If I recall they integrated iTunes into Catalina's Finder, but I've neither use Catalina or Big Sur so I can't reference what those were able to do and the state of feature set, all I can observe is what I have with Monterey and it isn't great in any aspect.
Music App, select iPhone device, it has a Sync setting button which opens Finder, essentially the same General tab in iTunes. When Manually manage music is checked, is asks to sync and erase, okay but there are no beats on the phone. Then it looks like it backs the phone up and erases the music library on the phone, none of these are what've intended to achieve. Typically in iTunes, you'd check manually manage music, switch to the Music Tab, then you'd either drag playlists from the sidebar (for me that'd have been folders from the Finder dragged into the iTunes side bar resulting in a playlist created from the folder name) then I'd drag those into the music list pane. But on Monterey, you don't have the same iTunes sidebar, you can drag folders from the Finder directly into the music list pane, it shows a copy progress bar but everything is greyed (no idea what is on it), there's a Sync Music check box, beats me why that is even there, it shouldn't be where' not in sync mode. The music list pane is supposed to be a free area drop zone for our tunes, both, individual tracks in folders for which playlists are created, but none of that **** happens here. It's the wrong behaviour, that's plain to see to me, bit it'd be hella confusing to a generic user. IDK what's going on with this, either they haven't finished manually manage functionality or they don't want us to use it like that or they forgotten about it and want loads of people to ring them up and ask for support.
It gets even more bizarre, you can then switch to the Music app after the Manually manage Music checkbox is enabled cos we've seen already the Finder ignores manually manage music, everything greyed out, expects you to sync, but with what..lol...
In Music app it has a sidebar, you can drag folders of tracks or albums to it, which creates playlists from the folder name, and contents, as expected, can then drag those Playlists to the iPhone device. But still is fsck'd up, the music list doesn't allow you to view the list on the phone as Playlists, only tracks, and all the sort options are greyed out in the view menu. You know you'd want to see the playlists in list view, and then rag other tracks from the Finder into them and you should be able to set the play order, abc title or track number but there's absolutely no user view type other that what they used to call it Song list view, a huge list of randomly ordered tunes,, no clue as to what playlists are on the phone. You click off the iPhone, an on to a Playlist on the sidebar in Music and then back to select the device and it re-populated columns that'd be previous unchecked, like Genre, I never list anything by genre, so I uncheck it but it keeps being re-added for instance.
I suppose the Music sidebar Playlists can be used as a temporary drop zone for organising prior to dropping them onto the phone.
IDK, what they are doing here, maybe even they don't know what they are doing, it's a poor setup, neither logical nor providing the most basic manually managed functionality.
Maybe Music and Finder iTunes are still a work in progress, think I'll get some feedback to them and keep an eye on any changes, if any, maybe they listening but doubt it.
There is an app I saw a while ago, forget the name, but something that allowed us to install Apple apps that had been removed, so maybe adding iTunes back this way to manually manage music the proper way is a solution for the time being...
I'll drop dome screenshots in so you can what we're dealign with:
