[Spoilers for Batman: White Knight [2017-2018] and Batman: Legends of the Dark Knight Issues 65-68 .)
Batman: Legends of the Dark Knight issues 65-68 (1994) feature a storyline called ‘Going Sane’ (which also exists as the trade collection Batman: Going Sane ). The story’s plot centers around the fact that Joker briefly beats Batman, and believing him dead, Joker retreats into sanity. Joker gains a regular appearance via plastic surgery and medication (which the narrative implies is prescribed for his bleached skin) and takes on the name Joseph Kerr. While Kerr finds love with his neighbor Rebecca Brown, a recovering Batman finds some inner peace in the nearby town of Accord with Doctor Lynn Eagles. However, both Joker and Batman return to their typical roles after a time. Joker does so gradually, as if sensing Batman’s recovery and finally upon seeing a headline about Batman (who returns by choice).
Batman: White Knight is a comic book series from 2017-2018. Its plot centers on an alternate history Joker returning to sanity via a mystery medication and then helping improve Gotham City. In this story, his real name is Jack Napier (taken from the 1989 movie Batman). Both Napier and the Joker personality have a Harley Quinn love interest. However, Napier’s love interest and eventual wife is the original Harley (Doctor Harleen Quinzel). While the Joker’s love interest is a woman named Marian Drews who went along with Joker mistaking her for Harleen. Joker returns when the medication no longer works to stabilize his mental health.
There are a few other differences between the two stories besides those that have already been pointed out in each respective summary. One such difference is the way in which Batman’s effectiveness is questioned in each story, but Batman: Going Sane relies on it more as a method to suggest time passing. Another difference is the way in which Batman: White Knight lays seeds for potential sequels (Such as the upcoming Batman: Curse of the White Knight [2019-Present]). Yet another bit of contrast is that most of Batman: White Knight is a flashback while Batman: Going Sane ranges between present day and flashbacks. Finally, there is the way in which internal thought takes more precedence in the narrative for Batman: Going Sane and external communication takes up the entirety of Batman: White Knight.
In conclusion, both stories explore how the Joker might regain a civilian life and a form of mental well-being before having it taken away. However, the ways in which each story goes about doing so is very different.