No, there's lots of calories in stool, but it depends on the type of food. For example, eating lots of fats and oils tends to "go through". On the other hand, rate of metabolism varies between people too.

Yes, this. These conversations about weight loss are so rife with spherical cows and people come to ridiculous generalizations because of it. Bodies are complicated and varied. "Michael Phelps eats 12kcal a day and yet he's not fat" is just a correlation, it doesn't mean anything. He's an extreme outlier of a person in many ways.

I was eating similarly in my 20s and 30s and in 20s I kept about 80kg but in 30s I got to 130kg :/

BTW there are diseases that reduce calories absorbed, you might want to get checked for colitis ulcerosa and crohn's disease. They have nasty side effects so better to know earlier even if you don't have the worst symptoms.

The body absorbs refined carbs very quickly. The glucose rush will increase insulin levels to very high levels and make you feel hungry again soon leading to the consumption of even more calories.