Meh. I find it charming. It's a product of passion not the product of hyper-optimised marketing designed to trick you into thinking it's good.

Use an icon pack, and it is very likely it has something different already there for Calibre. I use candy icons, and I like the Calibre "logo" in this icon pack.

If you meant the splash screen when it starts up, this can be turned off in the settings.

Otherwise the core app's UI looks fine to me personally, though some of the plugins make some, unusual, choices.

The UI is a mess of buttons and menus strewn about everywhere. I'm not complaining, Calibre is a great project, but let's not kid ourselves that the UI is even mediocre.

The last thing anyone needs is “visual” “designers” shitting up our useful applications.

Stick to your todo list apps and stay in your lane.

This is such an aggressive way of saying something unhelpful. Visual/information/interaction. design -can- be an important part of an app team. I also think calibre is clunky and many of their interactions inelegant. That it’s also ugly is not irrelevant - reading is or can be an aesthetic experience too. I’m grateful it exists but like Anki I really wish someone with real design skills could help them polish the rough edges - that would make it a pleasure to use rather than just ok.

Some designers are definitely terrible (e.g. whoever made the mind numbing decision to use hamburger menus in Gnome), but plenty are good at their jobs. Go and watch some Tantacruul videos on YouTube.