I'm sorry, I was not thinking. Space-before formatting does not work at the beginning of a section (or document).
Did you try centering the page vertically under Layout?
Align text left or right, center text, or justify text on a page - Microsoft Support
In that support page, see Center Text Vertically

You can fake out space before by having your text not at the start of the section; put a blank paragraph before it. You will end up with the space taken up by the blank paragraph and the space-before formatting for the new one.

For space-before to work at the beginning of a section, it needs to be in a Frame.
Space Before Heading at beginning of page - Using Frames