name of bridge
埇 is a rare kanji whose core meaning is tied to a specific proper name: a bridge. Its standalone meaning is essentially 'name of a bridge' and it is not used for general concepts.
埇 combines 土 (earth) with 甬, which likely contributes the sound. The exact historical development is uncertain, but it is probably a phono-semantic compound used for a place name.
The earth radical 土 beside 甬 suggests a structure made of earth: a bridge. Picture an earthen bridge named 埇.
For ヨウ, imagine a bridge over a calm pond where you see your own reflection: 'yo' as in 'your own' -> ヨウ, while standing on the earthen bridge.