That's perfectly okay that you cant see how it could look dated. If you wish to have a productive conversation you should probably open your eyes and look a bit broader, perhaps by not minimizing things to their absolute minimum and thinking about that. you reduce the entire UI/UX as "in a frame" because the rest of it is about the actual content and font, which are literally the most basic need that the rest of the discussion is what actually matters
The ebook reader on calibre is literally a frame with almost no border. There is nothing to discuss regarding UI/UX. There is nothing extraneous. You can’t even see the frame if you go full screen.
Unintuitive toolbars, takes an unnecessary amount of clicks to simply highlight a sentence, and resizing the window or moving it to a different screen reflows the content unintuitively.
Like everything else in Calibre, it has all the features I want to have and then some, but actually using them is always just a little bit more complicated than it needs to be.