In the 2017 series, Scrooge McDuck is a sworn enemy of Santa, and doesn't allow him to visit his mansion and bring gifts. The details of the animosity between Scrooge and Santa are unknown.
Santa has not made an appearance in person yet, but a drawing of him appears on Webby's string board. Based on that drawing, in this universe he is an anthropomorphic brown bear with a white beard, dressed in a red robe and hat.
In Last Christmas!, his appearance is shown to be more polar bear-like based on an inflatable decoration Scrooge destroys after finding it.