re: Cleaning a dirty spot on an otherwise new(ish) clean roof

I would get a mild detergent/ degreaser and spray it on and let it sit and then hit it with a hose sprayer. See what that does.

There’s something called soft washing, maybe can check that out.

But there’s lower pressure washing and then there’s high pressure. You could probably use very low pressure (wide nozzle) and be fine if you are careful.