how do you gain motivation to lose weight?

I think everyone needs to find their own reason to commit, the spark that lights the fire. That tends to be quite individual.

For me, the main two, maybe three, were:

1. I had high cholesterol, didn't want to take a statin. I figured I'd already given up enough cognitive bandwidth to chemotherapy, and brain fog is a possible side effect of statins.

2. I looked around me, and noticed that others around me of similar age (59 at the time) who were overweight/obese and inactive tended to have noticeably worse quality of life than those who were even moderately active and close to a healthy weight. The overweight and inactive people tended to be sick more often, get sicker when they were ill, need more surgeries, recover slower and with more complications, need more $$$ drugs, not be able to do fun things that involved more than minor walking or stairs (music/art festivals, stadium events, etc.), couldn't eat/drink some of the things they found tasty (because of health conditions or drug interactions), paid our more money hiring services (that the active/slimmer people could still do themselves), and more. I knew which group I wanted to be more like!

3. I had some other health issues that were being aggravated by my weight (knee pain, for one; borderline to high blood pressure, etc.). This was more a realization along the way during loss for me, probably, as I saw them begin to improve, rather than something that sparked my loss at the start.

But other people have different motivations to commit to weight loss: Being a better role model for their children, being more attractive, putting dangerous health conditions in remission or close (such as diabetes or fatty liver), etc.

After that initial spark - the thing(s) that flip the switch in a person's head from "I wanna" to "I'm committed" - this is what I think:

Make a plan that requires a minimum of motivation, willpower or discipline to keep up. Don't try to lose weight super fast (unless weight itself is a health crisis). Don't rule out all of your favorite foods. Don't shut down social life to eliminate temptation. Don't adopt a punitive, miserably intense exercise routine unsuited to current fitness level. Those things are optional. Being overweight is not a sin we need to expiate by suffering.

I don't know about you, but I can't possibly stay "motivated" for the entire rest of my life. Instead, I needed to find a manageable, reasonably pleasant (at least tolerable, practical) new set of routine habits, both activity (exercise + daily life) and eating. It needed to be able to continue almost on autopilot when other parts of life get complicated (because they will).

For myself, I said I wasn't going to do anything to lose weight that I wasn't willing to do to stay at a healthy weight long term, ideally permanently, other than a sensibly moderate calorie deficit for weight loss until I reached a healthy weight. (I'm now in year 8 at a healthy weight, after around 30 years previously of overweight/obesity. So far, so good. ).

Yes, we have to make changes in our life patterns, both eating and activity. But losing any meaningful total amount of weight - let alone keeping it off - is going to take time, many weeks to months, even a small number of years for some. That puts a premium on finding a sustainable, manageable new routine. Finding that routine may take a certain amount of "motivation" to do some experimenting and practice the new habits, but the easier it is, the higher the odds of long term success.

Just my opinions, though.

Best wishes to you for finding your reasons to commit, and those new habits. IME, the quality of life improvement is way, way worth the effort.