Hi! The easiest engine for GBA dev right now is Butano, but it requires C++ skills.
Don't underestimate yourself though! With the right learning material (e.g. book or video tutorial) it's possible to gain some C++ language experience in a few weeks, then you'd still have 1-2 months left to actually make something for the jam :)
We have a dedicated Butano channel in our discord too for help with the engine itself.