For the vast majority of global airports, a single runway does just fine. With a runway of adequate length, a facility can perform around 35-40 operations per hour, which includes both landings and takeoffs. For most airports, this is honestly far more than enough, as the vast majority of airports do not have more than this number of flights departing and taking off per hour. The only facilities that do require multiple runways are those that are among the largest global hubs, those that require the additional capacity to support more flight operations each day.