[Vuejs]-Passing a prop to child component isn't working on Vue 3

You shouldn’t use .value in template with refs of top-level properties. The value is automatically unwrapped for you (note: make sure the toggle in the top left of the docs is switched from "Options" to "Composition" for link to correctly work).

Simply remove .value and your code should work

<TheSidebar :sidebar-state="sidebarState" />