Star Wars: The Rise of Skywalker continues a retcon The Mandalorian most recently set concerning Endor, Jakku, and the fall of the Empire. In the final film of the Skywalker saga, the old Empire was a key plot element, most notably involving the destruction of the second Death Star during the Battle of Endor. Though it had been previously established by Disney's canon that this conflict was not the end of the Empire, and rather the battle in question took place on Jakku, this has been changed and emphasized in two pieces of recent Star Wars media, once again in order to fit the story set forth by the most recently released film in the series.
Much like in real world history, it is to be expected that when a ruling government falls after a period of civil war there is to be a battle that will remain forevermore as the difference maker. In the case of the Star Wars universe, the one that marked the end of the Empire previously was the iconic Battle of Endor. The destruction of the second Death Star and the death of both Darth Vader and Emperor Palpatine were initially the Empire's grand conclusion, planned or otherwise. Their forces scattered without their leaders and a new government could rise from the ashes. Prior to the Disney takeover, it was just assumed that Endor was the Empire's final resting place in the official canon.
The story saw some revisions when Disney took over, citing the Battle of Jakku as the definitive end of the war and the Empire. Jakku was said to act as the Empire's last stand, where all of the remaining Imperial forces would hold their ground and fight valiantly for their supposedly slain Emperor. This choice was made to tie into both Star Wars: The Force Awakens and Star Wars: Battlefront II, which both featured Jakku. This decision has once again been backtracked, as The Rise of Skywalker and The Mandalorian have elected to return the story back to its original form, putting the spotlight back on the Battle of Endor as the Empire's end.
Both Star Wars: The Rise of Skywalker and The Mandalorian season 1 refer to the Battle of Endor as the end of the war and the tyranny of the Empire, while making no reference to Jakku. The reasoning is not so dissimilar, given that Endor and the second Death Star were very important to the story of The Rise of Skywalker as well as the post-Empire world in which The Mandalorian takes place. This, of course, does not remove the Battle of Jakku from canon; it simply downplays its importance in the grander scheme of the universe.
All in all, this is a retcon that is important in some sense, as the fall of the Empire is a huge event in the Star Wars continuity. However, at the same time, it's a piece of information that is only as important as it needs to be given its context. It may be important in universe, but from the outside looking in, it is more or less a piece of information that is relative. The Star Wars universe is a big place, and the reach of the Empire was large and looming. Certainly some regions may consider different events and battles the important ones in their defeat. It could all very well be changed again in order to fit a narrative set forth by one of the many upcoming Star Wars movies on the way.