All the food he eats have sweetness in common bread, plain pasta, various fruit, yogurt,crackers, soft cheese and breadsticks
We humans are animals of habits, we like what we know and repetition will consolidate feelings.
I am not sure having the "safe" (and safe from what ?) food is helping.
What I suggest you try is this:
For a week - and I know he has a sister so you need to talk to her and tell her she is part of a secret plan - hide all the sweet biscuits, crisps, chocolate, and even the crackers and breadstick, they are as processed as they get.
During that week, change the meal dynamics, don't make them about him. Don't try to offer new stuff with that body/face language which is worried from the start he won't like it. Make family meals about family. Change the settings, so if you usually eat in the kitchen , clear the dinning table and set the table for all of you. Move a chair to make room for his high chair or put a booster on a normal chair. All of you sit together, without making a fuss about him eating or not, Maybe during that week, don't make "one pot " dishes such as stew or pies , but have a chicken breast, a schnitzel, a battered fish (all possibly homemade to wean him for the processed food taste and additives if he has any) , and next to it, a couple of potatoes, and some veggies, but single. Also consider taste. Make your vegetables delicious using extra virgin olive oil, coarse salt, fresh herbs. Consider slicing a pumpkin and roasting it with garlic, fresh rosemary, salt and oil.
It is not a punishment, it is adding stuff and new taste. Even the yoghurt, if he usually has a sweet tasting one, have good quality real plain yoghurt, to which you can add a bit of jam, with some frozen berries which you let melt and simmer in a small pot on the stove.
For breakfast, move away from sweet cereals (cheerios) and other processed food. You can make pancakes one morning (250 flour, 3 eggs, 1 tbls oil, pinch of salt, 500 ml milk) or even a homemade cake. The problem is the processed food, even seemingly innocent food such as crackers and breadstick.
You need to increase the variety, even if he won't touch it. Let the home family have different food every day, a wider variety of vegetables on the table, go for new food, such as homemade meatballs in tomato sauce.
Have the meal together and try to ignore him, and focus on a family chat, talking about plans, don't ask " do you want to try" or " see if you like it" or " you want something else" . Just leave the dish in the middle of the table and put a spoonful in your plate, your daughter's , then your son, before moving to serving your husband. Sit down, say enjoy, and start eating and talking about a radio talk, your sister's cat or whatever, but the food or him eating/liking it. Talk about going to the park later or making some craft. Have your daughter say at some point " this is nice, mom" . Show him everyone is eating it, have some, enjoying it.
While you cook and prepare food, have him with you, standing on a chair put safely against the kitchen top (with back of chai\r against furniture) and while you cook, nibble here and there, take a bite of ham, dress your tomato salad and then talk "hum.... what does it need, a bit more salt /parsley, basil....," and have him add a pitch, mix, taste again and say "perfect "
When it comes to fussy eating @lucaluxes you need to take action on two fronts, the meal times dynamic and increasing the variety at the table. This mean that for a week, you don't cave in and jump to offer alternatives.
Do some reading . I strongly recommend this book
www.amazon.co.uk/First-Bite-How-Learn-Eat/dp/0007549725/ref=tmm_pap_swatch_0?_encoding=UTF8&tag=mumsnetforu03-21&qid=1612903548&sr=8-1
and spend some time on pubmed reading medical papers on fussy eating.
www.ncbi.nlm.nih.gov/pmc/articles/PMC6398579/