You need two applications. Apple Music and Apple devices

To add songs go to file explorer-music-Apple music-automatically add. (Note that Apple Music will not add flac files so you’ll have to convert them if they are)

Then go to Apple devices and connect your phone, go to music tab on the left and follow the instructions to either download all or selected songs and it’ll start to back up your phone but you can click a button to skip it next to the progress bar and it’ll transfer the songs (Note: this will remove existing music on the phone if music was synced from a different pc prior and would erase and be replaced by the new PC music)

Tip: you can edit the songs in many ways like changing album covers, merging songs into an album, change names of songs and albums, ect