What, in fact, is a person, and what is his value?

Hello Rabbi. I’ve come across an interesting philosophical question, and I’d love to hear your opinion.
From the moment of fertilization until the eighth week, the human being is a “fetus,” but from the eighth week onwards, after the development of the brain, the fetus becomes “negative” and at about this time, according to the halakha (“40 days the soul enters,” etc.), they tend to be more lenient in certain cases of miscarriage.
Maimonides also says that the image of God in man is his mind.
My question is, what value do people with mental retardation, insanity, or in short, any disorder or disease that makes them think they’re on Mars and go crazy? That, in essence, makes them mindless?
Is it more valuable to save Einstein from a burning building than an ordinary person, who is probably less intelligent than him?
If intelligence is essentially the essence and image that exists in a person, then the difference between a person and a cat is essentially the same difference between a very smart person and a person with a disability?
Is the value of retarded people proprietary (their guardians) or like the value a person has in themselves (for which we kill animals and not people, respect other people and care about their well-being).
The rationale here is actually quite strong, even though intuitively it is very difficult.
I would love to hear your opinion.
thanks