This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 垨 is uncertain. It visually combines 土 (earth) and 守 (protect), but the original semantic or phonetic role of these components is unclear.
The left side is earth 土 and the right side is protect 守. Picture a mound of earth protecting something, but the overall meaning is unclear.
For シュ, imagine a shoe protecting a mound of earth: shoe -> シュ, and the earth 土 is guarded 守.