Chapter 1: Playing the Game opens with a brief description of Castle Ravenloft, if you want to be able to go in without already having heard that.

More seriously, Social Interaction Example at the end of the section on social interactions includes some relatively minor spoilers about several NPCs and a conversation that happens with one of them, including the temperament of at least one.

there are several boxes containing notes that expand on specific parts of the dialogue that hint at the NPC's temperament, though as that is influenced by the way that the party behaves it's... eh....

not great, but not the worst

imo much more seriously, Exploration Example at the end of the section on exploration reveals a possible twist, depending on how the dm runs the game, as well as a memorable secret passage and a trap inside Castle Ravenloft.

and finally, Combat and Damage Example technically contains some mild spoilers, though if the first few lines were removed imo it would not. It is, again, set in Castle Ravenloft, but the example is detailing a combat encounter with a small group of monsters that are a kind that most players would probably expect

There's some incredibly minor location spoilers for it, though they're nonspecific enough that i'm not nearly as mad as I am about the exploration example in particular

Of the four I've listed here, the combat and damage example is the only one I wouldn't say is explicit cos spoilers

primarily because it doesn't feel like there's anything that defines the scene enough that you'd know what was coming if you played the module

there are some minor hints as to the location it takes place in, but they are vague. It's not great, but it's nowhere near as bad as some of the others

anyway

wanted to warn anyone who wants to read the new 5.5 handbook but has not played cos and wants to unspoiled