Please consider making the Preview Window persistent even if it has nothing to show.
I was wishing for this for awhile but never requested. Now that I am testing the new Stage Manager feature in the MacOS beta this is even more important. Stage Manager moves new windows to the front and pushes the current window aside. The user can option to re-arrange, but that is only good if the windows persist. If a window disappears (like Preview if it has nothing to display) the user must manually keep re-arranging.
All my cards are heavy latex (not mathjax) so I am constantly Previewing after making changes to my cards.