My 19 months old boy doesn’t know how to suck from a straw. Is that normal? Any parents face the same issue too? How can I train him to suck?

Use sippy cup as a means to transit from teat bottles. Once you notice that he is able to suck slightly, introduce the straw. Buy those bottles that don't require alot of effort to do the sucking. I use Tommie Tippee and found it better than Pigeon or Avent. Dun stress over this, eventually he will get it. My son only know how to drink from a straw bottle around 17 months. My daughter manage to do it at 1yo. Every kid is different.