While Frozen 2 may seem to neatly conclude all its plot lines, there are many possibilities and theories regarding where the story of Frozen 3 will go. At the end of Frozen 2, Anna realizes she has to destroy the dam in order to restore peace in Arendelle. At the same time, that releases Elsa who rides the water spirit to Arendelle where she manages to freeze the flood and save the kingdom. After reuniting with Anna and Olaf, she explains that she and Anna are the bridge between the people and the magical people. This seemingly tied up the sisters' story, leaving Frozen with an uncertain future.

https://screenrant.com/frozen-3-movie-story-theories/