This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
愹 combines 忄 (heart/mind) with 容, which likely contributes the sound. The exact historical development is uncertain.
The heart radical 忄 beside 容 suggests an emotional state, but the specific meaning is unclear.
For ヨウ, imagine a heart 忄 that is as calm and accepting as a container 容: the calm acceptance cues ヨウ.