How does Shadow Sneek Attack Progress? Will it work with Strategic Strike?

Two question here. I am currently playing an Investigator in a Pathfinder 2e game. Thinking about going Shadowdancer.

A. How does Shadow Sneak Attack Progress? Is it just 1d6 forever, or does it progress on 11th and 15th levels?

B. Can it stack with Strategic Strike as Strategic Strike is not Sneak Attack?