Hugs. I can sense your frustration.
Honestly, all you can do is provide a good diet. It's your job to provide healthy balanced food and his job to eat, you can't make him eat.
Under 12 months he shouldn't really be having cow's milk as a drink from a cup or bottle, it should really be formula until 12 months, but I can see that he is almost 12 months so perhaps that is why you give cow's milk, please note though that it is not as nutritious as formula so if he is not eating solid food he may do better with formula which is made with balanced nutrients and vitamins.
Either he is going through a phase of teething giving pain which means he is just off his food and his appetite will return, or he has less of an appetite overall (this does happen at 1yo) and you will see a more prolonged phase of less appetite but he will still be well, or you may need a tweak to your eating routine. if you'd like to post your EASY times and what he is eating I may be able to offer some suggestions.
My main advice is to take a step back, there is absolutely no point in getting yourself wound up about this. He is not going to starve himself, he knows he needs food to live and you can trust he will eat a sufficient amount. This is not something for you to be angry about, it just won't get you anywhere (other than more angry). If you shout or deny him food you risk damaging your bond, take a breath and ask yourself if it is worth that? If he is squirming in his chair the chances are he wants to get down anyway, so why not just let him down and move on to the next activity, walk away and count to ten if you need to but when you go back leave the frustration of non-eating behind you and enjoy your time with him.
WRT good eating habits. A good diet is provided by you. This is your role. If you feel that there is too much bread stop giving it. That's it. If there is really no problem with how much bread he eats then give it without trying to get him to eat something else first. Bread isn't unhealthy, it's not like he's eating gummy sweets all day yk? But you decide how much is a reasonable toddler portion (I'd say half a slice) and serve it with his meal and do not give more.
Table manners are another issue. Just as with other aspects of our LOs development and the BW ethos, we need to be respectful of our LOs as little human beings, and to expect what they can manage at each stage of their lives and development. It sounds like your LO is squirming in his chair and refusing to eat... so I would look at lack of appetite at that time, maybe he needs to wee or poo and the chair position is not comfortable for him (mine used to sign toilet at that age and I'd get him out of the chair and he'd use the potty and then come back to eat happily and sit nicely once he had relieved himself), lifting him down saying something like "I wonder do you need to use your nappy/wee/poo? Lets try again in a few minutes" or perhaps he already needs a nappy change?
Honestly using a firm voice or shouting is not going to help, it will rapidly become a power struggle which you can't win.
If he doesn't like spooned food stop using a spoon for a while - this doesn't mean he won't be able to eat soup as an adult it just means right now he wants finger foods and to self feed.
If he wants down from his chair I'd just accept meal time is over, pack up what you made into tubs and pop them in the fridge.
if you feel bad about the waste reduce what you offer. One piece of food on his tray/plate at a time. When he has eaten it serve a second piece. The rest is in a clean serving dish so the food can be wrapped and kept until later or the next day.
Whilst it's ok to try again in 10 mins just in case he did need a wee or something, I would not keep trying in 10 mins and another 10 mins. Just do it once is my suggestion. You do not want to be feeding all day long. Meals at set times and ok if he wanted to go off for a few mins then shows he would like to come back fair enough for a few times, observe and see what his reason is, game interrupted? Nappy? Something else? Learn from those observations and adapt the routine if possible. If not then just offer at set times, once and that's it.
more hugs xxx