❔ Cannot convert lambda expression to type 'Activity' because it is not a delegate type error

public class MemberStats
{
    [BsonElement("userID")]
    public ulong UserId { get; set; }

    [BsonElement("Activity")]
    public List<Activity> MessagesPerDay { get; set; }
}

public class Activity
{
    public DateTime Day { get; set; }
    public int Messages { get; set; }
}

 if (Stats.MessagesPerDay.Contains(act => act.Date == DateTime.Today))
 {

 }