This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
僘 combines the person radical 亻 with 敞, but the exact historical development and original meaning are uncertain.
A person 亻 beside 敞, a component that suggests openness or spaciousness. The kanji may hint at a person who is broad-minded or expansive, but its meaning is unclear.
For ショウ, imagine a person showing (ショウ) a broad, open gesture: show -> ショウ, though the meaning remains uncertain.