It is absolutely normal, he hasn't learnt how to chew yet and food is not moving in the mouth. Next time you eat, try it, put something in your mouth without chewing , it won't go anywhere unless it starts melting. No wonder he starts crying .
Some kids learn fast, other take more time and that's fine.
Chewing will produce saliva which will lubricate the food, make it wet and easier to swallow. Chewing also means the tongue moves the food to the back of the mouth, as opposed to liquid when the tongue pushes milk/puree to the palate and from there down.
Now that you know the why, make some foods which are wet, such as a very soupy risotto, it will be wet, and there will be just enough texture to stimulate the chewing movement.
Or prepare some soups, with a bit of baby pasta in it.
Don't fall for the baby junk food, so ultra processed it does melt, but will give baby a preference for artificial taste. Melty puffs are just Cheetos with some powdered vegetables to be able to list them on packets. The same with rusk or veggie sticks.
Braise or roast your vegetables (no salt), such as zucchinis cut thinly lengthwise, and you can put a small piece on a baby fork. When. you start with fish, either boil it and keep some of the water so you can add a teaspoon of it with some melted butter to make it easier to eat.
Cook the lentils or chickpeas in a small pan, with diced carrot, celery , onion, some water, and then mash it with the back of the fork. It will be solid and wet at the same time
He is 6 months old, plenty of time to first learn to chew and then use hands.