I think non-verbal is confusing things, isn't it? The cause of this can vary so much in autism. It can be a reaction to stress/anxiety, and therefore affect people who are otherwise able to express themselves articulately (e.g. on another day, with another person, and/or in writing). It could be somebody who struggles to express themselves at all but they understand everything, they just have different ways to communicate (which of course represents a huge barrier). However, it might also be a reflection of the fact somebody has very little understanding of language or the world in general. These are totally different situations but may all come under the banner of autism.
Using "non verbal" as a marker for severity of autism is really unhelpful.
I know when I was younger, autism tended to bring to mind somebody who had severe learning difficulties, who may remain "childlike" in many aspects into adulthood, who has little understanding of the world and therefore cannot do many tasks for themself and will always need care because for instance they do not recognise danger as simple as crossing a road.
It seems this presentation is behind much of the fear around autism, particularly going back 20 or so years, feeding into things like the Wakefield vaccine scam and various other fringe movements (many of which still exist), the whole narrative that autism is an awful, terrible thing which ruins lives. The search for a cure and cause/identifier specifically so it can be eliminated. Autism Speaks. ABA as a brute force method to eliminate autistic behaviours. etc.
That's a problem because of course, autism isn't always like that, and arguably the cause of the most difficult of those issues is the learning difficulties, not the autism (if I understand correctly, please correct me if I'm wrong). You can completely understand somebody who is autistic without learning difficulties feeling upset at the idea they might be considered something to be eliminated.
Therefore the group of autistic people who are able to express themselves, whether only online or in person, started speaking out to represent another side to autism, without learning difficulties (or with a less severe type of learning difficulty, such as slower processing speed, which is not the same as a lack of processing ability). And that has led to a shift in the public perception of what autism means, and a whole lot of autism positivity, which is helpful but can lead to a skewed perspective, just in the opposite way.
But then there is another side too that muddies the waters in between. Because many children and adults with autism, without necessarily having learning disabilities, can struggle with meltdowns, (that doesn't mean tantrum, but a complete sense of overwhelm resulting in a loss of control) that are so disruptive and/or violent that they can restrict life very much - certain situations, places, actions, foods, textures, sounds, a whole load of things that will be different for different people - must be avoided in order to help avoid or reduce triggering meltdowns, other family members or teachers or anybody interacting with the person (esp child) have to be aware of interacting in a certain way, e.g. for a PDA presentation avoiding or minimising demands - although yes, it's true that autistic preferences and needs are no less valid than neurotypical preferences and needs, it can be extremely difficult and alienating being autistic or having an autistic child, it can take a lot of time and effort to understand what the specific person's needs and triggers are, and they might change over time. While in theory somebody with autism could live a perfectly happy life when neurotypical demands aren't being made of them, that's not how our world is set up and so being autistic is always going to be difficult in some ways.