19 month old assessment. So please help!

I am of the opinion that your worries about your child's language / speech development are a bit premature. I would suggest you to take up your concerns with your child's paediatrician who will be in a much better position to tell you if there are reasons for you to worry. If the paediatrician feels that there is a requirement of assessing his speech development, you may consult a speech therapist for that. On your worries about any spectrum disorder (autism?) you may undertake an autism assessment test through a good clinical psychologist. I think it is possible even online. While all these will give you a fair feel of your son's mental condition, I would still say not to get into any kind of labelling of it yet. Let the paediatrician come out with a relevant assessment report, even verbally. In the meantime, if possible, try to reduce his screen time further and involve him in the day-to-day activities at home in an age-appropriate way. When he gets involved in what is happening around, it is likely that he will pick up speech faster.