ᐅ What is the best type of paint to use for painting the shed?

In a multi-family house, I have this shed setup.

Some work needs to be done on the shed. The lower part is always green now, which is not easy to clean off. How should one proceed here to protect the wood? How can the green be removed, and which type of coating or paint would be recommended afterwards?

I would remove the weathered layer mechanically, perhaps with a wire brush. If it is already soft, it won’t harden again, so there is no need to sand it down until nothing is left. There are clear primers available that are fungicidal and similar; I would use one of these as a primer. Some are even organic. The coating could be a thick-film stain. If you can see the wood grain through it, it’s a stain. If it is completely opaque, then it is a paint. Thick-film stain is somewhere in between. I would stick to the same type of material that is already on the surface. Clean thoroughly, let it dry, and lightly sand it. Use a fine grit, just enough to scuff the surface. I cannot see any significant cracks in the coating. If you want to preserve the lower edge longer, and the rest still looks good, you could install a metal strip as protection down to the sound material.
Best regards, Gabriele