With stopping the apocalypse being the end goal for both seasons one and two of The Umbrella Academy, it would make sense that a potential season three would follow in their footsteps. Harlan isn't able to control his powers in 1963 and without proper training, this could lead to a potential apocalypse should someone set him off in the present day. However, with the introduction of the Sparrow Academy, it seems creator Steve Blackman is looking to ditch the apocalypse so it's probably safe to say that no, Harlan will not be the harbinger of doom. Instead, according to Inverse, Blackman is looking to shake things up and we can expect that "there will be more destructive family madness."