Adipose tissue retains an epigenetic memory of obesity after weight loss

I am pretty sure the only way to reduce the number of cells is liposuction

Worse than that. Subcutaneous fat (which is the one you can trim off with liposuction) usually expands relying more in cell expansion and not in hyperplasia. Visceral fat on the other hand, is way more likely to involve hyperplasia and you cannot use liposuction against this type of fat. This is also the fat that is very hormonally active and increases the risks of diabetes, heart disease, cancers, strokes.

I've been wondering about that. Like all cosmetic surgery liposuction is looked down upon.

But maybe it can also be a useful and healthy weight loss strategy?

Despite being looked down on, it's still very common. I know several people who have had liposuction. The results are only temporary. Everyone I know that has had this procedure has rebounded back to their original body weight within 2 years.

Is it unremovable because it's inside the core muscles and near internal organs?

Right. A surgeon can't just stick a liposuction tube into the abdominal cavity and poke around. This would be major invasive surgery with a high risk of complications, far worse than leaving the adipose tissue in place.

See the second half of this video: https://www.youtube.com/watch?v=Bav_IBsuXEM

Visceral fat is literally enclosing the intestines, major blood vessels, organs, etc. of the abdomen.

Nevertheless, it is possible to surgically remove this sheet of fat that's covering your organs, it's called an omentectomy. But it's a big surgery, and done only in case of cancer, not for weight loss. That is, in humans: https://pubmed.ncbi.nlm.nih.gov/29367725/

Liposuction is actually a very risky procedure, at least in relation to its benefits. For example, fat embolisms in liposuction occur in 8-9% of patients that undergo the procedure. There are other risks that are non-trivial as well.

If I had to advise a patient on whether they should consider liposuction vs gastric bypass vs GLP1R agonists, I would tell them to not consider liposuction in that equation at all.

As with most cosmetic surgery, risks like these are downplayed by practitioners (willfully and otherwise) as well as by people in these social media circles.

This doesn't mean liposuction shouldn't ever be used, however. It can have good uses in reconstructive surgery, for example, where fat is sucked up to be used in reconstructing a different area. In this case, the potential reduction in morbidity and restoration of function to the patient, or increasing their autonomy, might make the risks associated with lipo worth it.