Big Sur's redesign is an unusable mess. Window borders are pure white. Contrast is non-existent, especially on buttons (both light and dark modes). Too much transparency, it's not just distracting - the menu bar is often unusable (depending on your wallpaper). Many builtin apps exercise too much freedom in customising the look&feel, everything is inconsistent. I understand this was done to bring the design language closer to iOS, or to make iOS apps feel more at home on the Mac. They are not - every time you run an iOS app, it really feels out of place.

Some of this can be remedied with accessibility settings. Most things will likely stay broken until someone at Apple calls for yet another pointless redesign that will break something else in return.