Other mistake: Rey pilots Luke's X-wing to Exegol from Ahch-to. However, the door to Luke's hut on Ahch-to was seen in TLJ to be an X-wing wing. It is even referenced as such in The Last Jedi visual guide which specifically states it's a wing from Luke's fighter. No way to fly it if it's missing a wing, and when it's lifted out of the water we see it has all its wings intact.
Catwalk
3rd Jan 2020
Star Wars: The Rise of Skywalker (2019)
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Suggested correction: The novelization explains that Rey repairs the X Wing, saying, "It was old tech, and it had taken some fast thinking and even faster fingers to get it flight worthy - the wing patched with the door to Luke's hut, shield panels scavenged from the TIE wreckage, and a hefty amount of rewiring."
The novelisation fixes the mistake but it remains a mistake in the movies as we see them.
Not everything has to be shown on-screen, Rey and Luke easily could have repaired the X wing.
It was never stated in The Last Jedi that the door was from Luke's X-wing, though... Not once. Nor did the door look like it came from the X-wing, and the X-wing looked intact during the brief shot where we saw it submerged in TLJ. If you need a secondary source to know about the error, it does not qualify as a mistake in The Rise of Skywalker. If anything, it's a mistake in the guide book (that the novelization of TROS tried to fix), not the movie.