I would definitely want to have a way to turn any such feature off (including with Preview).
I also worry that the widget that Preview would get wrapped in might cause issues with future Qt incarnations. We had a border coded around one of the widgets (which I'm thinking was Code View) that caused all kinds of problems with Windows dark mode until it was finally removed.
But as long as there's a functioning "turn off all visible focus decorations" preference checkbox, I'm not opposed.
