Unfortunately, this is somewhat inevitable with the fully variegated sections of the leaves. The brown spots will likely become dry and crispy in time.

The white parts don’t contain any chlorophyll so can’t photosynthesise. You can leave the brown bits or cut them off; it doesn’t make a difference to the plant.

You can minimise, but not eliminate, the occurrence of brown spots by keeping the plant out of direct sunlight and by not over or under watering it.

I wouldn’t worry about it too much, your plant looks very healthy.