Gaining

a heavy bottom half thighs, bum, hips and lower belly?

I want to have a subcutaneous fat, cuz it's soft and jiggly😋. Any tips to gain only this kind of fat?

Dairy, dairy, and more dairy. A lot of people on here mention heavy cream as the holy grail for gaining subcutaneous fat, and I can attest to that!
I drank a quart of heavy cream throughout the day on top of my normal diet for about two months, and saw a 30lb gain. It pretty much all went to my lower belly, ass, and thighs, most of it being subcutaneous.
Heavy cream isn't for everyone, though. Some can't get over the thick texture, others mix it. For me, I'd just gulp it down and chase it with something sweet LOL.

I would think for just expanding the stomach...simply eating & drinking larger quantities and more often would do the trick. Sort of the opposite of dieting and shrinking the stomach. The type of food might play a role in where it ends up, along with genetics...but hard to say where that ends up between different people.

Cocktails, daiquiris, mixers, slow the metabolism. Regular Sodas and averaging 4-6 glasses of water to avoid dehydration, gout etc.

Emotional connections to certain foods...whether they remind you of good times with friends or family or comfort you when missing friends/family.