Hi, welcome to the forum!
One easy way that I use to manage what to sync and what not to sync is the "check" or "tick" column, which you can activate in the main panel. You can tick or untick tracks in groups, so it's pretty quick. Then create a library filter for ticked or unticked or both, and sync only the filter you want. (You could create an auto-playlist to get the same effect; filters work very similarly.)