Is there always a physiologically, physiological difference between level 1 and 3 autism?

Allistic here! For context I have adhd, and have always been interested in psychology. Since adhd is so intertwined with the autism media sphere I’ve learnt quite a fair bit about it as well. So it’s got me courioud about a few things namely the question in the title.

I have, however never found a way to properly word this question and find answers about it online. I understand theirs a different diagnostic criteria for level 1 and 3 autism, and the support needs are different, but is it always still only due to autism? If that makes sense. For example, is someone who requires higher supports need always diagnosed with some other commorbidity? IE, genetic disorder that impacts IQ, and if so is this what separates someone with level 1 and 3? Or is it really just the disorder itself manifesting in drastically different ways.

I know that it’s sort of hard to say because autism is almost always comorbid with something else irregardless of level but I figured you guys would know far better than I would ever. Thanks again, feel free to correct me on anything if it was insensitive or not explained correctly!