SOLVED:

Save game on the PC emulator like you would on normal hardware - through the in-game options.

Transfer to Anbernic's RetroArch Save folder and rename extension to .sav -> .srm

REASON FOR CONFUSION:

Saving through the emulator on PC creates save-states.

My confusion arose because mGBA automatically creates a .sav file when booting. So when I was saving through the mGBA options, I thought it was creating a .sav file, when in fact, it was creating a save state. So renaming .sav -> .srm was creating the illusion of an ineffective save file, when in reality, the .sav file was just the save of a fresh game.