Considering that Act 3 is the climax of the play, how can we defend that Fleance's escape from the murderers is the turning point of the play? Note: it's from Macbeth

True.

Explanation:

Turning point is the moment in a plot where there is a "turning point" in the story, something big that can modify the course that the narrative was taking and presents an advantage or a disadvantage for the protogonists or antagonists of the story, however it always presents itself as a major climax-related event.

In Macbeth the climax happens at the moment when Macbeth is close to killing Banquo. At that moment Fleance flees trying to secure his position at court. This escape is the turning point in history because it gives the necessary resources for the prophecy that Banquo received, at the beginning of the story, to be fulfilled.

Banquo's prophecy stated that he would be the point of origin of a line of kings, but that he would not be able to be king.