Usually, the blur means that the picture is being manipulated to a certain extent, in order to make everything more 3D like; and in the case of Pokemon Detective Pikachu, there’s a real good quotient of blur.
Which leads to you, the audience, seeing that classic 3D blur that folks have been talking about for ages.
The backgrounds especially benefit from the blur, which more than likely explains the impressive depths of this film’s picture.
If your eyes get tired, or your mind gets curious during a 3D film, you’ll want to slip those glasses off and see what the world looks like without the aid of polarized lenses.