Help with solids?

For a little background, I'm fostering my nephew. There is a history of autism on both sides of his family, I'm pretty sure my sister smoked weed while pregnant with him, and 100% did vape while pregnant. I have no idea if any of this is linked to the struggles we're having now with his development but maybe it can give some insight. He is in the birth to three program (for those of you who don't know, it's a program to help babies with development from birth to 3 years of age). They said it's too early to diagnose but he shows a lot of the signs for autism.

Is there any advice anyone can give that helped them get their baby to eat anything other than formula and oatmeal? he loves sweet things and will have purees that aren't vegetables or meat. he will have them with oatmeal mixed in but it can't be too thick. If it's even slightly too thick he will gag and sometimes dry heave or even vomit. Same goes for anything like puffs, solid fruits or vegetables, chunky purees, etc. He absolutely will not have it. I'm desperate for anything that could possibly help my sweet boy overcome this.

Thanks in advance 💜