Rewatched the trailer and some breakdowns.
I think it’s focused on Elsa taming nature/elemental spirits and making peace/amends with the Northuldra tribe (which parallels the Huldra, which were hidden people/elves or something).
We have Nokk (aka Nix, a la Once’s Nix) being the water spirit. Book being the spirit of water and a horse ties back to Scandanavian folklore, etc. However, it dovetails Greek myth as well (Poseidon, god of the sea makes horses).
The lizard thing looks to be the fire spirit. The wind spirit seems to be some Moana type thing. Earth...I don’t know.
A definite thing is the theme is exploring Elsa’s Powers, which appear may be tied to her mother in some way.