Looks like large pavers. We live in wet winter country - PNW so moss etc is a routine thing here. We use the product Wet and Forget on our smaller pavers which works on moss & grime pretty well. Not all moss is green - it’s black mold looking too. Wet & Forget comes in concentrate or a sprayer container. Needs to be put down when pavers are dry & be able to stay wet for @ hour - so no spraying in sun or heat. Rain comes & washes black away & moss dies so it’s not immediate result but is seen working after the first rain. Not sure how successful this would be in less rainy climate. We buy it at Costco - product is popular here. We did pressure wash our pavers once using a round attachment that gives a much softer wash than the angled hard spray of the angled spray point of pressure washing. We were afraid the pressure washer would lift all the sand filler between the paver joints.

ETA: we’ve never sealed our pavers but it is done by some. Need to clean first & I think it’s not permanent so must be redone every few years.

We live in northern Ohio, so we get a little bit of everything weather wise. Wet and Forget looks like a pretty good option. We do have plants around the patio. Do you think this would be safe to use without killing them as long as we’re careful not to directly hit the plants?

Looks like pressed concrete to me. There are certainly products to seal it and power washing should be fine as long as you aren’t too close.

Yes, must be careful of plants - says to wash off right away. My husband does this job for us & he uses a spray container that you can carry by strap over shoulder & it has a pointed wand for spraying. This stuff works on cement & other things too. He sprays our sidewalks. This is less labor intensive - easier on the back - than pressure washing & of course uses much less water. We have 1,100 sq ft of pavers so that’s a lot of water & time. The trade off being having to wait for results. At this time of year, we don’t yet have our patio furniture out anyway.

ETA - Per BobH note about ok as long as not too close - that’s exactly the reason we don’t want to power wash & were nervous even when using that large round attachment that spreads water out & softens the stream / jets. We’ve all seen concrete that’s had the top layer taken off by too aggressive power washing. Same with house siding & paint!