Two parts
Wikipedia’s bonus list files Genichi Sojo’s Bathhouse Quest and #2 (双城厳一のお風呂探訪♨ and #2). The first extra already has a room. This page exists so a search for the second part does not invent a plot. The joke sits next to a man who died on Datenseki.
Volume extras also include Soya Sazanami’s Memories, Begone!. Official chapters stay on VIZ and MANGA Plus. Extras stay in the Jump Comics object. See omake.
Official chapters live on VIZ or MANGA Plus. This desk does not host pages.