In East Asia and elsewhere, the Ghost Festival and the Filial Piety festivals are one and the same. The Ullambana Sutra talks about how the Bikkshu Mahamaudgalyayana was able to perceive his mother languishing as a Hell-Being, this concerned him greatly, and of course wanted to relieve her suffering. The Buddha told him that through the an act of generosity to all the monks & nuns--all sentient beings--the dedication of merit of all Bhikshus would relieve their parents and ancestors for seven generations from their rebirth in the three lower realms as Hungry Ghosts, Hell-Beings, or Animals.
This may appear apocryphal, metaphorical, or even superstitious. But if we look at this through the lens of modern-day Zen practice, what does this mean we do? By being generous in whatever form that may take to all beings--even our parents or family members we may not get along with so well. Our practice will generate good will (and merit) that we may dedicate to family members both alive and dead, and all sentient beings to relieve them of their suffering. The parent-child relationship may often be fraught, but parents are responsible for our life, looked after us throughout our youth, allowed us to go forth and live our own lives (including both wise and questionable decisions), and may require our affection and help as they age. Parents--and all sentient beings--are in this human realm==and all experience suffering. They deserve our filial piety and help as Bodhisattvas.
Min'Ui Maitri gave the talk on August 30, 2023 at One Mind Zen.