You can save rare hunts for later in Monster Hunter Wilds, so you can come back for that Rey Dau gem when it’s convenient
As a gamer, I’d say: “To save a monster on my map for future hunting, I hover over the beastie on the big ol’ world map and then press A on my Xbox controller (or F if I’m using keyboard). This kick-starts a new quest creation. After that, another press of A does the trick, and I opt for ‘Save as Investigation.’ Instead of diving right into a field survey hunt, this action creates a quest that I can pick up later from Alma at the quest counter in the Investigations section.