According to TV Line, HBO Max only ordered one season of Young Justice following its run on DC Universe (which is now the comics-exclusive platform DC Universe Infinite), and that hasn’t changed.
In 2019, six years after its initial two-season run on Cartoon Network ended, Young Justice returned for Season 3 on DC Universe, and Season 4 followed a couple years later exclusively to HBO Max subscribers.
Assuming that Young Justice Season 4 was indeed meant to be the expectation-defying final season on HBO Max, the Season 4 finale certainly made it seem like Season 5 was a possibility.
As such, the outlet has heard that there are “no current plans” for Young Justice Season 5.