Reddit reviews Building A Family: An Mpreg Romance (Frat Boys Baby Book 2)

There is a fine line between the fictional portrayal of a nerd dialed up to 11 and the fictional portrayal of an autistic person. Not sure if the realities are all that similar, but when filtered through a story they kinda are. Also, you have lots of magical retarded people in fiction. (Sorry if that comes out offensive...but that's the best way to describe them. They are rarely described well enough for it to be clear eactly what is different about them.)
So, if you are OK with characters that read as autistic but aren't explicitly that broadens it.

The webnovel The Salamanders has a main character that reads as borderline autistic. Late in the series it's hinted another character wonders if he is as idiot-savant. (It's a fantasy world without the concept of autism)
In A Turn of Light by Julia Czernedas there are two retarded/autistic/brain damaged (It's unclear) people who are more in-tune with the magic of the valley. That sort of thing is common.
Not fantasy, but the cyborg construct protagonist of The Murderbot Archives reads as vaguely autistic. (And I met an autistic person who agreed.)
In the specialized Mpreg Gay Romance Building A Family: An Mpreg Romance (Frat Boys Baby Book 2) there was an odd take on the Cinderella story...a love story between a rich architect who read as autistic to me and a poor landscaper. I mention this one because oddly it is one of the better portrayals, and an interesting twist on the power dynamics of Cinderella stories.
Gate of Darkness, Circle of Light by Tanya Huff had another one of those magical retarded people.


EDIT: Oooh, Just realized the recent book One Word Kill has a character that is clearly supposed to be autistic.