The vibe I get from reading the Keto sub and many publications and articles about Keto on the Internet is not that calories in calories out is not a thing, but that it's really hard to measure the "out" part.
The "in" is not a problem: you eat a gram of carbs or protein that's 4 calories, you eat a gram of fat that's 8 calories. For the calories out its not so simple, there are approximate formulas you can use based on body composition (which is also not easily and reliably measurable unless you have one of those DEXA machines somewhere near) but those also vary a lot depending on what you eat since fat molecules (eg C55H98O6) require more energy to break down compared to carb molecules (eg C6H12O6).
If you read Gary Taubes' Good Calories Bad Calories he digs up studies where they fed an 800 calorie low carb diet to one group and an 800 calorie low fat diet to another. They found that while both lost weight the low fat people were generally hungry and miserable but actually lost less weight than their low carb peers.
So I guess what I wanted to say was if people say "CICO is not a thing" they either interpreted all that information wrong or they actually mean that conventionally taught CICO is not a thing (e.g. a normal adult uses about 2000 calories a day so if you eat less than that no matter what you eat you will lose weight). Companies that sell highly processed foods and sodas usually fund studies that aim to prove things like that because for them it means they can advertise that you can eat as much as you want of their product and not get fat as long as you don't eat more than the 2000 (plus minus a few hundred depending on your height, age, etc.) or so calories. In reality it's not as simple as just eating less and as always, everyone is different. For some people eating 1200kcal works, for some Keto works, for some just eating the same but doing IF works - and I bet there's dozens more diets that work for different people, but overall I've yet to meet someone where every single diet works (eg Keto works well for me but my girlfriend can't do it because she loses too much weight - so she eats the same things I do with carbs added back in for one meal and a couple fruits as snacks to maintain a healthy weight).