Seen it in the snow dome of extinction if this information helps

Note for everyone on the Dododex, these do not only spawn on Ragnarok. They spawn on Scorched Earth too.

they also spawn on extinction from what i’ve seen

They spawn on lost colony aswell

They only spawn at nighttime. Then you grapple with the new drake hook and then play three separate mini games before feeding it mutton

Both umbra and lumina spawn on scorched earth. I've tamed lumina and searching for umbra but I have picked him up on the dino finder.