In The Rise of Skywalker, we see a massive fleet of Star Destroyers, which, for all intents and purposes, I will call the Exegol Fleet, due to the fact that they are seen on Exegol. One shot near the beginning of the movie shows hundreds of these ships, called 'Xyston-class Star Destroyers', according to Wookieepedia, side-by-side, in the air. Also according to Wookieepedia, there were approximately '1,050' of these ships. But, since Wookieepedia is notorious for being inaccurate, I do not accept this as true. How many of these ships were on Exegol?
According to the film's official novelisation, there were "tens of thousands" of Star Destroyers on the planet.
Around it, more mountains broke the surface, resolving into massive Star Destroyers, half again the size of the Destroyers from the days of the Empire. A single, giant obelisk erupted also, a navigation tower that would coordinate their final ascension. It unfurled like a metal flower, exposing its petal-antennae to the violent sky.
More ships rose—and more and more—until tens of thousands hovered in the atmosphere.
“For a generation, my disciples have labored,” Emperor Palpatine said, his voice dark and deep.
Kylo’s heart was racing. So much power. A starfield of Destroyers. The largest fleet the galaxy had ever known. The rumors were all true. Exegol was a world populated by the Sith Eternal, true believers in the dark side of the Force, devoting their lives to this.