I think there is a difference between entering a space where any person (autistic or not) is alone and changing that environment without speaking to them to check. Open plan offices are definitely more challenging, but there needs to be a fair balance where accommodations are made

For example, not every workplace would allow headphones to be worn without a prior discussion. It's about being mindful and considering what can be done to improve an environment. That is shared between an individual and the employer. It's okay to have needs, the point is they shouldn't be dismissed

Yeah, to me, asking first is a basic courtesy regardless of whether anyone in the room is autistic. For instance, if the window is open, maybe someone is experiencing hot flashes, or is feeling nauseous. It makes sense to ask rather than assuming the window is open for no reason.