To create an app bar that is pinned to the bottom of the page, you can use the -Footer parameter.
New-UDAppBar-Children { "Hello" } -Footer
Relative Footer
A relative footer always stays at the bottom of the document. If the contents of the page do not take up 100% of the screen height, the footer will be positioned at the bottom of the view. If the content is greater than 100% of the screen height, the footer will only be visible when scrolled to th bottom of the correct.
A fixed AppBar will show even when the screen is scrolled. It will remain stuck to the top. This example creates an AppBar that is fixed with a div that is 10000 pixels high.