If it’s oily, you could try dish detergent as a first step, scrub it gently, to keep it in the same area, then blot up crud, and rinse. I’ve sprayed oxyclean on leaf stains on concrete with decent results.

Don't know where you live, but I know here I get spots like that from birds eating berries and then pooping dark plops. If dish soap doesn't dissolve it, I've used 30 second outdoor cleaner on mildew spots with no ill results on my flagstone. If it's an oily spot from something, it probably won't work for that, but maybe a dryish paste of baking soda and water might absorb some oil.

Thanks ladies. I washed with dish soap...we’ll see what happens....

Fingers crossed

Dawn dishwashing liquid won't hurt. A former landlord of mine restores historical brick and masonry. His crews use liquid Tide dilute in water ( I don't know the ratio). They wet the stone/brick first, then scrub with the soap solution using stiff bristled nylon brush. Then rinse.

Perfect! Thanks for updating.