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

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

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

Dododex doesn’t say but I’ve seen both dragons in astreos

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.

I used a dino finding mod ok valguero and a umbra was detected but despawned. The logs did say a umbra spawned, but showed there were 0. This may be a bug, but if your on valguero, you can find Umbras!

According to all of these tips, they spawn on more maps than just Ragnarok