“I wonder, is weight gain/maintenance hereditary?”

Yes.

And, that does NOT mean that you have no control.

You have genetics, and you also have epigenetics.

Epigenetics are how your environment (which you control to large degree) change which genes are expressed.

Look, I won’t pain too rosy of a picture here: you may have conditions that are difficult to overcome, and which may require medical guidance.

But even if you do, guess what?

Getting your nutrition in balance will only help whatever efforts your doctors are making.

If you give your body half a chance, it will begin to heal itself.

That is what the body does.