I found Unofficial SPIKE Prime Block Guide, which has following details:
And if you open the SPIKE app (2.0.0 or newer), the light blocks were completely changed:
Is anyone able to explain why?
With the introduction of the SPIKE Essential set, this element was introduced:
It's a matrix of 3x3 colored LEDs. It has similar functionality as the 5x5 light matrix on the SPIKE hub, so the same blocks to control it are used. The word blocks are not modified that heavily, the only thing that is changed is that you need to specify an additional parameter to indicate which light matrix you want to use. M1 is the matrix on the hub itself, A to F are the ports you can select where you have the external 3x3 matrix attached. You'll also notice that if you change the parameter from M1 to a port, you'll be able to select more colorful options for the image to display, as the 3x3 external matrix supports a range of colors, while the 5x5 on the hub is monochrome.