Syncing lossless Music files to iPhone

Pre-iOS 13, I had been using a feature that I stumbled upon by chance, which seemed undocumented and yet was extremely useful: the ability to download (sync) Apple Lossless files from iTunes onto my iPhone *despite* the fact that I am simultaneously an Apple Music subscriber. Here is how it worked:

1. I ripped a music CD (that I owned) to Apple Lossless files.
2. I added the ALAC files to iTunes (on macOS 10.13 High Sierra). Apple Music would process those files, and would usually match & add them to my Apple iCloud Music library (keeping the ALAC files locally available).
3. I kept iTunes open and connected my iPhone to my Mac via USB.
4. At that moment, when I went to Apple Music on my iPhone, when I would tap to download the record to my iPhone, it looked like Apple Music was downloading the files (those little red circles) but actually what it was doing was copying them from my computer's library instead (blazingly fast). I could check that with absolute certainty in Settings / General / iPhone Storage / Music: the size of albums in iPhone storage was unmistakenly that of lossless files.

So let me recap again - it's like the best of both worlds:

• When my iPhone was connected to iTunes and the album had locally-stored files in my Mac (notably lossless files), Apple Music on the iPhone would seemlessly sync the lossless files to local iPhone storage.
• When my iPhone was not connected to iTunes, the exact same action would download compressed files from Apple Music's cloud service (as would be expected).

And now, either with iOS 13.0 or a subsequent release (I couldn't say which), this behavior is broken. I cannot download lossless files anymore from my Mac, they all come compressed from Apple Music's cloud service. I tested both with macOS 10.13.6 High Sierra's iTunes library, and 10.15.1 Catalina's Music Library, and Catalina doesn't resolve the issue.

This is a real pity, because for some music and/or instruments there really is a difference in timbre (in jazz music the trumpets are slightly muted / maimed by Apple Music) and I can't enjoy my CDs anymore while getting additional music from Apple Music.

Have any of you used this feature before? Have you found a fix to re-enable syncing of locally-stored Music library files?