Currently, left clicking just replaces the current TomTom waypoint. It would be nice if it just added a new one - so I can go through the list, left click the ones I want, and then just go from waypoint to waypoint.

This is a good idea. Once I get world quests unlocked for Dragonflight, I'll look into making this adjustment. Or, at least, adding it as an option.

This feature will be added in the next released version, 11.0.2.15