You can download the GBA4iOS ipa file from below download links. Then after that you need to sideload using cydia impactor. GBA4iOS only supports gameboy advance games. If you want to run games from other platforms then do checkout Gamepad.

GBA4iOS IPA Download

Note: If the download link is not working then inform us in the comments below.

Go to Settings»General»Device Management or “Profiles and Device Management”. Here you will have trusted and untrusted profiles of apps. Trust the profile of the app you just recently installed. Now launch the app. You are good to go now.