This is an absolutely charming game, with cute graphics and solid mechanics! :) I can't wait to purchase this someday!
May I ask what game engine you used to make this?
Viewing post in Goodboy Galaxy DEMO comments
For Goodboy we're using our own engine written in the Nim programming language, but the easiest way to get started with GBA dev nowadays is the Butano engine (requires some modern C++ skills).
Check out gbadev.net for a full list of resources!