What causes iPhone music transfer issues with Windows?

My itunes library folder (using win10 and Apple Music) is 33.5gb. When I use Apple Devices to transfer to iphone using only checked songs, I get only have 2.62 gb in music data on the phone although more than 90% of songs are checked. At present I have 69.33GB of unused space on new IPHONE 16e. If i try to sync entire music library, I get the message it requires an additional 50 gb.---on top of the 69 gb that is free on the new iphone se?? Odd when the entire folder in windows only has 33.5 gb. I don’t understand this. Any one have an idea??

[Re-Titled by Moderator]

Original Title: win to iphone music transfer problem