It sounds like you're looking for the Weight Gain Game hosted on .
If you remember a specific title or creator, I can help narrow it down further. weight gain game on itch.io
Just to clarify: there is no single official game with that exact title. Instead, "weight gain game" is a common tag used by indie developers for interactive fiction, RPGs, and visual novels focused on expansion, inflation, or transformation themes. It sounds like you're looking for the Weight