Syncing iPhone X from Catalina syncs ALL my music every time, taking ages
I've only recently upgraded (I use the word loosely) to Catalina.
Now, every time I sync my iPhone X - for example if I have added a couple of songs to the Music app on my iMac - it copies every song from the iMac to the iPhone, taking ages.
With iTunes it just used to add the new songs to the iPhone X and so syncing only took a few seconds.
Why is this happening and how can I make it just copy the updated songs/info to the iPhone, not every single thing every single time?
iMac Line (2012 and Later)