Although Vikings: Valhalla ended with its third season, it set up a couple of storylines for a fourth season that wont happen. After Vikings ended with its sixth season, Vikings: Valhalla arrived to explore the stories from the final years of the Viking Age. As such, it followed new characters from different backgrounds and with different goals, though all of them linked through their Viking heritage. Vikings: Valhalla introduced viewers to Leif Erikson (Sam Corlett), his sister Freydis (Frida Gustavsson), Harald Sigurdsson (Leo Suter), King Canute of Denmark (Bradley Freegard), and Emma of Normandy (Laura Berlin), brought together due to the St. Brices Day massacre.
https://screenrant.com/vikings-valhalla-season-4-plot-details-setup/