Lope de Vega (Lope Félix de Vega de Carpio) is generally thought to be the most prolific playwright of all time. About 400 of his plays survive, and the general opinion is that he wrote between 1500 and 2000 in his lifetime.
Google on the name “Vega” and phrases like “most prolific playwright” for fuller details.
Of course, nobody can be sure about things like this. Vast quantities of literature have been lost over the centuries. Also, many literary efforts never get recorded because they are too poor to be accepted by publishers - but they have been written, none the less.