An updated FAQ on the official Hogwarts Legacy website has confirmed the popular wizarding sport Quidditch won't be playable in the game. You'll still be able to get about the school of witchcraft and wizardry aboard a broomstick, but the flights won't get competitive with a Quaffle and Golden Snitch.
In the sport's place, you will be able to take Flying classes and compete in broomstick races. The full response explains that "Quidditch is not playable in Hogwarts Legacy. However, broom flight for traversal and broom race challenges are part of the game. Players can also fly brooms to explore new and familiar locations surrounding Hogwarts Castle." It had been hoped Quidditch matches would be playable in Hogwarts Legacy, but once the title was revealed as single player only, dreams of online bouts were dashed. Now we know we won't be putting up with Beaters and Bludgers at all.
The Quidditch pitch at Hogwarts has been part of a few pre-release trailers, so perhaps your custom character will at least be able to watch the sport from the stands in cutscenes. If the game chooses to stick to the canon set up by supplementary book Quidditch Through the Ages, though, then you shouldn't expect the broomsticks in the game to travel at too high a speed.
As previously pointed out by Screenrant, broomstick travel wasn't known for its speed until the 1920's when the Cleansweep Broom Company came along. Prior to its formation, brooms were generally made by hand and said to be quite uncomfortable. They were quite slow too, and since Hogwarts Legacy takes place in the late 1800's, we shouldn't be expecting to travel from Hagrid's hut to the castle entrance in a matter of seconds.