This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
盶 combines 目 (eye) with 元, but the historical development and original meaning are uncertain.
The left side is an eye 目, and the right side is 元 (origin). Imagine an eye looking back to its origin, but the meaning remains unclear.
For ゲン, picture an eye 目 looking at the origin 元 of a gen (ゲン) in a bottle: gen -> ゲン, though the kanji's meaning is uncertain.