What's the syntax for `signon-ui`?

I’m looking for a really easy to use basic window that can render webpages correctly, so that I can provide better-looking screenshots (for things like `talk.commonmark.org` is offline. · Issue #74 · commonmark/commonmark-web · GitHub). signon-ui appears to provide this. However, I’ve been unable t ascertain how to invoke its GUI:

PS /home/RokeJulianLockhart> 'https://www.downnotifier.com/list/overview?id=915677' | signon-ui
QtWebEngineQuick::initialize() called with QCoreApplication object already created and should be call before. This is depreciated and may fail in the future.
^C