Complex sentence: Cartridge adapters such as cheat devices made before the release of Super FX games like the Game Genie did not have a connection to these previously unused slots, so Super FX games could not be plugged into these devices.
Split into simpler sentences: Cartridge adapters such as cheat devices made before the release of Super FX games, such as the Game Genie, did not have a connection to these previously unused slots. This meant that Super FX games could not be plugged into these devices.