How did you successfully lose weight?

Restricting calories.

How you do this is a continuous negotiation process with yourself - remove certain foods, skip meals (i.e. intermittent fasting / time-restricted feeding), don't eat carbohydrates, eat whatever you want as long as it's within a daily calorie limit etc. Pick the one that's easiest to follow.

The thing I do right now to lose weight is keep a spreadsheet and every day I write down my weight and the calories I consumed that day and I aim to stay below a certain average calorie count. This means that I get to lose weight and eat whatever I want, and I can have high-calorie days as long as I offset them with some low-calorie days. I prefer flexibility over trying to eat super strictly perfect 100% of the time.

I went from 89kg to 71kg in a space of 1.5 - 2 years. The main thing is to just eat less (and avoid processed food as much as possible). My main principle was to eat fresh and eat less. I did a good amount of exercising too in the start, but I observed that even without significant exercise, as long as I ate well I did lose weight. I put not many conditions on what I ate, except mostly avoiding sugar and sugary foods at home (still ate them in social situations).

Reduce carbs to as little as possible. But eats lots of protein instead. Fats too. Bread, pasta and rice are 'killers' for me.

One doctor I know eats lean beef in 500G to 1KG amounts. I don't know that I could do that.

And only 'above-ground' vegetables, so no carrots or potatoes (which are stores of carbohydrates), but eat broccoli, peas, beans, tomatoes, etc. instead.

Big impact: No soft drinks anymore, just water

Big impact: Reduce sugar intake to max 25g a day

Medium impact: interval fasting (16/8)

Small impact: Fitness. I do a lot, but frankly fitness just doesn't have much of an impact on losing weight.

I'm 34 and keeping my weight of 80kg that way for many years now.