Lets say we make a bread using flour with ~350 calories in 100g.
We make a small bread with like 220g of that flour. Add bit of oil, sugar, water, yeast and salt.
How many calories would that bread have in 100g? Is it 350(kcal in flour):100?
Lets ignore calories in sugar and oil, for simplicity.
This question cannot be answered. You cannot ignore those other ingredients, because oil in particular has very high calorie density - 15g has 120 calories. There’s also no way to determine how much is in 100g because the ingredient ratios and amount of water will affect that. The only way to calculate this is to add everything up, weigh the loaf, and then calculate the fraction of total calories.
If you just want to know the “flour fraction” of calories i.e. only how many calories come from the flour, you can weigh the bread and calculate the fraction of the loaf that constitutes 100g, and then calculate how many calories all of the flour has and take the same fraction of that. That wouldn’t be very useful though, because it wouldn’t give you an accurate calorie count.
It might be worth reading up on how calories work, how to calculate the calorie content of your food, and which foods are high or low in calories.
The problem is made easier by the fact that bread is relatively homogenous. You’d just have to measure all of the ingredients, sum up their calories, weigh the resulting loaf, and use e ratio of weights before and after baking to calculate the calories per 100g of baked bread.