Since the most advanced versions are fan games (EXE files) rather than standard GBA ROMs, you must use a compatibility layer to play on Android.
It’s not an official Nintendo or Game Freak game. No official Pokémon game carries that exact name. pokemon indigo league gba 2021 download for android
Open My Boy! It will scan your device for .gba files. Tap on IndigoLeague.gba . The game will boot up, and you will see a custom title screen featuring Ash and Pikachu. Since the most advanced versions are fan games