Transfer Music Files?

So I have some music files in my iTunes library on win10. Plug in my phone via USB and it shows up in iTunes. If I do this booted into MacOS, I can drag and drop files from my library to the mobile device. However, in wn10 iTunes I can not do this. Tried googling and got many instructions that I can not follow (many say to enable File Sharing in a menu that shows the different file types ON the phone, but such an item does not show up. Many reference copying from one window to the other, except I can only have one window open in iTunes.

Oh, when I tied the drag and drop I have a cursor symbol with multiple document with a number of them lower left and a “+” sign, like add to something.

Any ideas?

I still use iTunes on an old Mac running Mojave. I cannot drag and drop songs to the iPhone but there is a function for managing music on the iPhone from iTunes. I can select albums, songs or playlists and transfer them to the iPhone. I can also backup the iPhone to the Mac, which is more comprehensive than an iCloud backup.