I was reading your question another time. Were there other symptoms than speech delay that you were thinking in the direction of ASD ? as I would be very hesitant to think about ASD when there’s only a speech delay.
My son spoke only 5 words when he was 2.5yrs old, he was just a late talker.
The son of my friend didn’t start talking till he was 4 yrs old, again just a late talker

Just keep up conversations with him do he can learn. Maybe suss out a speech therapist for extra assistance

Start speech therapy now. If it is ASD, early intervention, the sooner the better. Also a Developmental Paediatrician and/or Child Psychologist should be able to diagnose. These are the steps I took with my child.

Get a second opinion and referral to the NDIS to support funding for speech therapy :). Good luck

Is he “talking” that is not understandable. It may be that his brain is very active and he thinks a lot faster than he can say the words and it results in bad pronounciation. Sometimes one person can decipher what the child is trying to say and another person can’t, You should apply to NDIS to get support with speech therapy and any other therapies available. You may also be eligible for other Govt. help.

Ask the paed to support you to access early childhood intervention through the NDIS so you can get some speech therapy

Just to reassure that all kids are different, some talk early some late. When son (now 14yrs old) was 2,5 yrs old he only spoke 5 words, he just started late nothing wrong with him. My 6yr old has Down syndrome and has a severe speech delay, she has speech therapy since she was 2yrs old or maybe even younger.

Talk him frequently take him in toddler preschool so he can socialize and communicate with his age fellows