Thousands of duplicate songs on iPhone

I have an iPhone 12 and an older Mac Mini running Catalina. I've had this issue a few years and gave up before but trying to work it out as it's annoying me again. I added music myself to iTunes on my Mac and sync those songs to my iPhone. This worked well until a few years ago all my playlists disappeared from my iPhone but the playlists were still on my Mac. The songs were still on my iPhone too, just not the playlists. If I go into iTunes and tick sync playlist it adds the playlists back onto my iPhone but then I have duplicates of thousands of songs. How do I stop this, can I delete all the songs from my iPhone but keep them on my Mac so when it syncs with my Mac again it adds them back but doesn't create duplicates of thousands of songs?