The (admittedly lacklustre) canon "evidence" I have scraped together for autistic Undyne (no c5 spoilers as I haven't played DR):
Tags: @bogos-bint3d, @justali-anne, @sharxxybaitxdd, @potatolord72
What it was based on: Papyrus is autistic coded. Alphys is also autistic coded. Undyne has close bonds with both of them and many autistic people find it easier to build rapport with other autistics.
Her aversion to cold and sweet foods could be a sensory issue.
According to Alphys, Undyne makes intense eye contact, which some autistic people do either naturally or as a result of attempting to mask (i.e. overcompensating).
She shows signs of ADHD (such as jumping between topics during discussions) which commonly occurs together with autism.










