Tony first i would clean with just distiled water or bottled water never use anything acidic or high alkiline most neutraul household cleaners should be fine. with a terry towel if its just small by hand .
its often the hardwater that has gone onto the floor thats made it dull looking.
As quartz tiles are man made and not natural here can lie the problem as a good tile should be as follows 95% quartz & 5% resin.
QUOTE BELOW.
all quartz tiles should be made with 95 % , otherwise they cannot claim the hardness, durability, or impermeability of a true quartz surface. MOST ARE MADE IN CHINA SO WHO KNOWS.
HOPE THIS HELPS KEEP IT MID PH