Question says it all. I've almost finished all the Crown Tundra (and the game as a whole) I only have this left, problem is I don't know how to get to it.
Once you complete the first 3 legendary clues (capture Calyrex, the Regis, and the Galarian Birds) and tell Peony, you will get a 4th called “They came from the ultra beyond!”. A cutscene will occur involving the ultra beasts when approaching the max lair, and you can now find the Ultra Beasts and Necrozma.
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