Press F12 to get the renaming criteria window - but the main window stays the same so I have two areas of renaming criteria (changing a value in one updates the other too). I expect the main window "renaming" section to disappear to free up space.
I'm thinking this might be a bug as the screenshot on https://www.bulkrenameutility.co.uk/Whatsnew.php looks ok.
I'm Windows 10 and have it in dark mode.