I also hate the blurred backgrounds.
Visually, it is incredibly distracting switching between clear <-> blurred, especially given how very frequently new popup boxes/windows occur in game - literally happens several dozen times within an hour of regular gameplay. Even worse when rapidly doing basic game tasks. Instead of drawing clearer attention to the new box/window, my attention is consistently diverted unconsciously to try to make clearer what's blurred. Our brains are wired to try to do that. Add to those substantial issues the fact the I can longer reference how much I have of something (coins, supplies, tavern silver, etc) when within the new box/window, as that info is completely obscured in the background.
The only thing I can think they were trying to do with blurring backgrounds for most everything was draw a player's attention quicker & more precisely to the new box/window (though, not sure why this was deemed an problem needing a solution). Unfortunately, their chosen method of change is incorrect visually & neurologically for accomplishing such a goal.
Having a thicker defined outline to a popup box/window, as well as use of contrasting colors between foreground box & background(s), is a great way to draw/focus attention - and without causing unnecessary issues.
Another good way, given this game's graphics/etc, would be to slightly dim the backgrounds relative to the topmost box/window. Game already displays that way when opening the quest windows. Could be wrong, but think that's the only current instance where it's done, or at least done well enough that I notice it. I do realize some are photosensitive to light changes (even slight ones), which can be very visually distracting as well. Therefore, it really should be implemented very sparingly at most.