Modern cameras (Sony, Canon, Nikon, Fuji) have an feature with customizable limits. This is the single best tool for eliminating blur/ISO confusion.

Here, the concept of "Blur ISO" flips. You need a to facilitate the blur. You want the sensor to be insensitive to light so the shutter can stay open longer without blowing out the highlights. In this context, ISO is the key that unlocks the blur effect.