Any Way To Restore Music Removed from iPhone by Apple Devices on PC?

I had built up a huge music library over years on my old PC, that PC was lost years ago but I still had the library on my iPhone. Today I tried to add one song (which I had ripped from a CD) to my iPhone via the apple music & apple devices apps on my PC (since apparently it isn't possible to drag and drop music from itunes onto an iphone anymore).

I chose the option to sync "selected artists, albums, genres and playlists" and seletced the one song I wanted to be added to my iphone. I clicked sync and Apple Devices proceeded to remove every single piece of music from my iPhone which did not originate from itunes. That's everything which had be ripped from a CD and so forth, thousands of songs gone.

Is there any way to undo this and why is it harder in 2025 to add non-itunes music to my iphone than it was in 2010?