I initially tried scotchbright backed sponges on mineral deposits from my shallow water well supplied sprinklers misting some windows leaving those extra hard water deposits that nothing seemed to remove. Desperation tried the scratchy Scotchbrite backed sponges... worked!

Now use them on all the exterior windows. Usually with stinky ammonia & water. Then hose it off and follow with a slightly damp miracle cloth, maybe a dry one too. Pretty easy and fast.
Reflective foil like tint on some of those windows really show up tinyest specs and they come out marvelous.

I'd be worried about the Magic Erasers ruining any protective coatings on your windows. If you do use them on your windows, make sure the pad is wet. A dry eraser will scratch your glass.

I'm curious what the "shotgun" fungus looks like as I've found odd-looking dark brown dots outside our house that I can't figure out. Can you please provide more info? Thanks!

Why not just use a window scrapper and scrap them off the glass?

The problem can be eliminated by using rot resistant mulches, like cedar or cypress...or covering existing mulches with the same. Itr doesn't hurt anything...nothing harmful but it does leave difficult to remove spots on light colored surfaces.
And it prefers sunny moist conditions...that's why it shoots it's spoors toward shiny or light colored things.
It's not new, but has become more of a nuisance since regulations are restricting burning and the kinds of things going into the landfill. Tree trimmings are ground up for mulch and the spoors may be in the wood.
Linda C

Have you tried ammonia & water? Ammonia is great at removing things.

I would get rid of the mulch.