Andrew. Dave is correct. The deck looks like gel coat. In fact the blue non-skid is exactly the same. Gel coat starts out smooth but in time the pores open a bit and it looks chalky. You can recover the smooth protective and shiny surface by a very fine sanding like polishing your car. This is good and bad. If you sand to much you will remove the gel coat and then you have just fiberglass. Here is s link to help.
https://forums.sailboatowners.com/index.php?threads/tips-for-a-great-buff-wax.117266/
The answer for some is to paint over the gel coat. For me I am resisting painting till I have to. My boat is not shiny.
Another challenge with our boats is if we rub a stain on the gel coat we can rub the stain into the gel coat. Then we have to paint. So try first washing with soap and water. Use a soft brush. Think shiny car body. This is the technique I would try first. I have gotten stains or what appears to be stuck dirt out of the non skid with just soap, water and a small brush. It is a labor of care.
If you are too aggressive you will be painting the boat before you need to. Not that it is bad just as the above link indicates not the first choice in the long run.
Welcome to the forum show us pictures of the boat and of your progress.
