I can totally sympathize with you! Toddlers are strong-willed beings, they’ve got their whole identity as individuals on the line!
My only advice is to try and get one step ahead if you don’t like how the current methods are working, outsmart ‘em by offering choices that are acceptable to you so they can feel some independence by making a choice, and you can be happy with whatever the outcome is. Sometimes we remember to do this ;)
Like @gussnarp, we have a rule with our 2½ year old about getting up from the table – when he’s done eating, he needs to wash his hands. So, if he gets up, he has a choice between washing his hands and being “done done” or sitting back down and continuing to eat. It helps cut down a bit the number of times he pops up, but offering a choice really really helps with the battle of wills that happens if we tell him to sit back down.
At restaurants we usually put him in a highchair if we don’t want to struggle, but at home and sometimes out, we want to be teaching him how to eat at a table in a regular chair.
When our son was one and a half, we had a down and out battle with him meal after meal about eating. Mostly about eating healthy foods that we knew he’d eaten and liked in the past. Meals tended to end in tears, always his, sometimes (more figuratively & frustratedly) mine. My husband and I learned / decided at that point that having battles of wills was causing all of us to lose, and not resulting in more healthy food being eaten, and once we lightened up, made the healthy food available but also things we knew he’s happy to eat (bread and milk alone are a pretty balanced meal for a toddler), he now maybe half the time is happy to explore other foods.
If he wants more bread, that’s an opportunity to say “I’ll give you another piece after you’ve eaten (or sometimes just “tried”) your broccoli and chicken.” Sometimes then he’s too full for the bread, sometimes he gets it.