A simple way to get floating groups centred (or at least create the same outcome) is to make the actual floating group the full width of the page, set as a row container, and transparent (i.e. no background style)…
Then just add a group inside the floating group, centre aligned, to act as the visible element.
You’ll need to use some simple custom CSS to stop the transparent floating group from blocking clickable elements beneath it, and ensure clickable elements inside it remain clickable, but that’s simple enough to do.