This has been fixed. See: https://grokipedia.com/page/japan_national_route_473

"Heavy rains in June 2023 damaged a stretch near Hachiji Town in Okazaki City, Aichi Prefecture, causing landslides that closed the route until full repairs on December 28, 2023"

Also 1 year ago, it seems another landslide occurred which is not mentioned in this wiki article:
https://www.openstreetmap.org/note/4768966