Scratches or Deposits ?
I can’t tell from the photos if those are patterned surface scratches from grit imbedded in the brake pad or bits of brake pad material transferred to the rim … or both!
I have found both conditions on some of my vintage rims - remedied (right or wrong) by wet sanding the rims with very fine 600+ sandpaper and a very light touch. It’s a time consuming process and kinda rough on the fingers, but the result is a pretty clean and smooth braking surface. Coupled with new pads, it seems braking efficiency is improved too.
BTW, I’ve also seen a SwissStop block that looks like a medium sized blue eraser marketed for cleaning up whatever it is that collects on the
sides of rims, but haven’t tried it FWIW.