This page explains how to complete the level 90 post-Endwalker quest "Newfound Adventure".
This quest is available if you have completed the quest Endwalker.
Starting the Quest
Talk to Tataru in the Rising Stones in Revenant's Toll in Mor Dhona to begin the quest. There will be a cutscene.
Speak with Tataru at the Diamond Forge
Check on the Exit to Revenant's Toll and say Yes to go outside, then go north to the quest icon on the map. Go into the door on the right and talk to Tataru to complete the quest. There will be a cutscene.
The Unending Codex is now available in Main Menu > Duty > Collection.
Next Main Scenario Quest
After you complete the quest, talk to Tataru to accept the next quest: Bountiful Ruins.