Likely answer

Thriller About a Kidnapping During a Neighborhood Party

The book you are looking for is "The Couple Next Door" by Shari Lapeña. This domestic thriller centers on Anne and Marco Conti, who attend a dinner party at their next-door neighbor's house. Despite using a baby monitor and checking in every half hour, they return to find their infant daughter, Cora, has been kidnapped, leading to a tense investigation that reveals dark secrets within the neighborhood.

Confirmed match: The couple next door by Shari Lapeña