I do get it, OP. However, your mistake is thinking that crappy food is better than no food. Problem is by doing so, you dig your grave at double speed. You not only reinforce a food preference, the artificial taste of UPF, but you also reinforce a behaviour, rejecting food, UPF will land in my hand.
In French, we don't even have a word for snack. Offer breakfast, then NOTHING , not a bite, not juice/mil/k,,, , only water and have him with you whilst you prepare a nice lunch.
Something easy, wet, that is tasty and doesn't require a lot of chewing, Baby egg pasta (Emiliane Barilla has a good range) in a rich broth with a knob of butter and a bt of real parmesan, The salty taste of the broth and parmiggiano combine with the fat taste of butter make it resemble the fat+salty combo of the melty puff (those are just Cheetos for babies if you read the ingredients).
Go shopping together, prepare a soupy risotto, again with butter and parmiggiano.
Make food that tastes good.
take a bag of mixed frozen berries, add 3 tablespoons in a bowl, microwave on high for 5 min, let it cool down and mix with Plain greek yoghurt.
Slice a zucchini length wise as thin as you can. Put on an oven tray brushed with extra virgin olive oil. Lay them flat, not touching one another. brush with more olive oil, sprinkle the tiniest amount of salt, cook at 180 until the thin part turns darker. Cut a tiny piece and put it on a baby fork. It is soft, moist, tasty.
A simple sole, cooked in a pan with butter is irresistible. No fish bone, no strong taste, it just melts in the mouth.
Often here , I see some whatever trust website being recommended. I looked at it, food looks vile, taste-less, effort-less, no wonder UK kids reject real food if that is what is presented on a plastic plate.
And soups? Why is nobody soups in UK? From mild to tasty, very clear to thick, with or without pieces, the variety is endless.
Leave the high chair or whatever seating is used in a corner for a week. Have him shop with you, wash the veggies with you, have him in your arms when you stir (safely of course), then have him sit on you, when you dig into it, and just dip the spoon in it or have a teeny piece on a fork. Just enough to touch his tongue, and stimulate taste buds. Smell is strong signal around food.
But you need to cut the junk (puff, crisps, rice cakes, rusks , baby cereal, cereal bars, ....) for 1 week .