The gas giant Endor is known to have 9 moons, and basing on the colour shown on the visual dictionary for Rise of Skywalker, I can surely say the moon that appeared in the background is either Vix or Gouuls.
https://i.sstatic.net/i4hKW.png https://pbs.twimg.com/media/EMp1RkvWkAUBjW5.jpg:large