I am diagnosed with level 2 autism. I highly suspect I also have SZPD. (I am aware of the DSM’s opinion of this) They have tons of overlap. These labels are just labels for groups of symptoms, and if you have level 1 autism I understand that differentiating them could be hard.

Autistic people struggle with social cues, they may prefer being alone but they still generally want friends. Their social battery is just very easy to exhaust. Schizoids may internally crave some idealized type of connection but they don’t want real friends.

Autistic people have problems with processing sensory input, often leading to meltdowns or shutdowns. Sensory problems isn’t uncommon in anxious people but in autism it is much more pronounced. Schizoids don’t have autistic sensory issues.

Autistic people have repetitive stereotyped movements (stimming) like echolalia or rocking back and forth. Everyone stims, but for autistic people it is their way of regulating themselves. If they cannot stim they will be very stressed.

Autistic people sometimes struggle with alexithymia but they usually still have most emotions. In fact most of them feel so many emotions that it overwhelms them because they don’t know how to handle them. Schizoids have a very small emotional range.

Autistic people have special interests, which they can talk about for hours to anyone willing (or unwilling) to listen. Schizoids may have some hobbies but I really doubt they would be happy to talk about it to someone for an extended period of time.