Best of luck with your goal.
My own experience with GLPs came only after I had already dropped from 145kg down to 75kg, yet I discovered they make maintenance far simpler. Every earlier attempt at weight loss had finished with me putting it all back on, but this time, 3 1/2 years on, my BMI is still in the normal range.
To my mind, this is exactly where GLP medications prove their worth: maintenance. Shedding pounds through a huge diet and exercise push is tough, but holding onto that loss is tougher still. If you use GLP drugs to lose the weight and then continue taking them, the weight generally stays off over the long term. Even surgery is not as reliable for long-term maintenance, though surgery can produce bigger total losses. Knowing that lasting maintenance is genuinely achievable is a strong motivator, particularly for anyone who has lost weight before only to regain it.
Responses to GLP drugs vary enormously from person to person. A small share, perhaps 5-10%, barely lose anything; others drop a great deal even on very small doses; and some run into side effects they cannot tolerate. The only way to learn how well they will work for you is to begin and raise the dose gradually, then hope for a good outcome. For the overwhelming majority, these drugs transform the treatment of obesity.
Typically tirzepatide produces roughly 25ish% weight loss over about a year, while reta gives 29%, so reta is somewhat more potent, though it likely carries a slightly higher rate of side effects. Since you are aiming to lose a large amount, reta could be the stronger pick, but tirzepatide is not far behind on effectiveness.
I understand the exercise problem. For someone who is unfit, intense exercise can be deeply off-putting, leaving you feeling so awful that forcing yourself to continue becomes extremely hard. The best way to begin and stick with it is to make it easy rather than hard. Back when I was still overweight and very unfit, I simply committed to a 5 minute walk daily. I made it so easy that there was no excuse to skip it, and almost no risk of ending up exhausted or unwell afterwards. Over several months I slowly extended the time, turned it into a habit, and eventually reached about 3 hours a day after several months and quite a few kilos lost, which made a big difference. Crucially, I avoided the aversive post-exercise fatigue I had usually felt when I had tried exercising before. The specific exercise does not matter; the principle is to lower the barrier so far that doing it feels effortless, you are unlikely to dodge it, and you have a real chance of making it a long-term habit. That said, you must still do that minimum amount daily or a set number of times each week. I did not even attempt walking until I had reached 115kg, because even then a mere 5 minutes left my feet hurting terribly. Sometimes, if someone is severely obese, waiting before starting exercise is sensible.
Eating well while on GLP drugs is wise, but they work regardless, simply by reducing hunger so you eat less. They probably perform better when not battling a high fat, high sugar diet, and they tend to nudge you toward better food choices anyway. Getting at least 1.5grams of protein per kilogram of body weight is sensible to limit muscle loss during weight loss. High protein intake also fills you up more per calorie than any other food, which helps with both hunger and losing weight.
