Congratulations.

I'm in my 40's. When I was in my late 20's I noticed that I'd started to put on some pudge. I'm 186cm tall and had been used to being very skinny and able to eat as much junk as I wanted. I'd been a long distance runner in school, generally active, but had slowed that down after getting a programming job. I weighed myself for the first time in years and I was 90kg. Not "fat" but not comfortable for me. I lost 20kg over about five or six months and have kept it off for about the last 15 years. I've gone up and down by a few kgs, but never went above 75kg again. I literally weigh almost exactly 70kg today.

The advice I give is generally close to what you've found. I didn't track calories or anything, but I weighed myself every single day, tracked it in a spreadsheet and consciously adjusted what I ate and how much I ate based on my average over the last week or so. Basically, if my weight was on track, I'd eat what I felt like and not worry about it. If it was trending up, I'd consciously make an effort to eat "less" than I wanted to; smaller portions, skip a meal, drink water instead of beer, etc. The further off track I was or the longer it was taking me to get back on track, the harder I'd have to correct. It involved the same shift in mindset, that I wasn't just losing weight, but achieving and maintaining a certain range was just part of who I was.

Like I said, I didn't track calories and still don't, but I did take a very data-driven approach where the results of my recent past actions determined my future actions. Basically, our bodies are bad at accurately signalling whether you have eaten enough or too much. Most of us, if we just eat when we feel hungry and eat what we think is a good amount, will get it wrong most of the time. We need to bring in external data to that feedback loop.

At some level, "calories in calories out" is right and it doesn't matter that much what you eat. If you are adjusting the quantity based on results, it will work. But of course, eating well really does make it easier. Eating more whole plant-based food and balancing your macros tends to make you feel fuller so you aren't fighting your own sense of hunger as much and keeps you healthier and feeling healthier and more energetic. It's hard to maintain the willpower over long periods if you are eating junk and your body isn't being nourished properly. You might lose weight but you can still ruin your health.

I'm also skeptical of calorie counting because there does seem to be some truth to "not all calories are the same". "Calories in calories out" works based on what your body actually digests and metabolizes. I'm not convinced that the calories in the food you eat match what your body actually gets out of that food, whether that's consistent across different people or even for the same person over time. Eg, I wouldn't be surprised if personal gut biome plays a large role here.

Similarly, exercise isn't strictly necessary, but helps in so many ways. I'd mostly recommend keeping it minimal until you are well into the "maintain" phase. I think a really common failure is when people get really into exercise, push it too far, then burn themselves out (or injure themselves) and crash out of the whole thing. Find physical activity that you enjoy and can do on a regular basis and don't overdo it.

The big thing that I feel is hard to get across to others sometimes is that there is a huge difference between "simple" and "easy". Losing weight and keeping it off with that approach is extremely "simple". But it's far from "easy". I've been doing it for fifteen years and it's something that I still have to work hard at basically every single day. I'm only maintaining my weight so it's not a huge sacrifice every day, but it's not easy to keep that level of effort up over a long period of time in the face of whatever other ups and downs you might have in your life. I get a bit hurt and frustrated when others downplay my efforts because I "look thin" so they believe it must be easy for me. (then they usually ignore whatever advice I give them in favor of the latest fad diet that their overweight friends are recommending because clearly their overweight friends must know more about diet and weight loss than me).