This pops once you do all the repair projects with the Gorlek Ore guy as well as planting all six Mysterious Seeds with the herbalist. Both the ore and the seeds count as collectibles, so I advise leaving this until you complete the Hand to Hand sidequest to reveal all of the secrets and collectibles on the map. That makes collecting everything a breeze (and lightning fast with the launch ability from the last area combined with spirit well warping).
To get the last one to show up, talk to the Moki above and to the right of the fire pit (that has air currents once you hit it with the feather).
This collectibles video now has individual timestamps for every collectible, as well as within which main area they are found, as a pinned comment.