Bleach,
Try it, makes the job 100 times easier.
Basically means you’ll be softwashing.
I started mixing thick bleach with water in a backpack sprayer for facias and gutters, it was the best move I’ve made.
That led on to buying a softwash machine from Ben at Rutland pumps, before I knew it, I was into the softwashing business as well. With a website dedicated to Just that, as well as my standard window cleaning one.
Try it, you can mix it to a low strength ratio, so there’s no risk of damage to plants/grass etc etc.
It makes the algae, dirt and lichen drop off, with a small amount of scrubbing where needed (depending on how strong a solution you go)