Can't sync my iphone music to my Win10 iTunes library

When I select Songs on my iPhone 13 Pro, I get a song list with many duplicate songs that play twice.

So I opened my Win10 iTunes, chose "file\library\shyow duplicate items". A list of duplicates appeared, and I deleted the duplicates from the library, leaving just one copy of each song.

Next, I synced my iPhone to my iTunes library.

The sync 'completed' almost instantly.

But my iPhone Music's songs list still has all those duplicates still on it, and each duplicated song still plays twice. It seems as though the iPhone is not really syncing.

What am I missing? I thought the master song list was kept by the Win10 iTunes music library, and I thought that 'sync' means 'sync my iphone to my Win10 iTunes music library". If so, why doesn't my iPhone sync to that library...and how do I get rid of these duplicates on my iPhone? There are far too many to go through thousands of songs on the iPhone, clicking one by one on each duplicate-listed song's "..." symbol, and choosing 'delete'.