Choose the "Convert File" option from the menu.
You don't need to search for risky "highly compressed" downloads online. You can compress your own legitimate backup using the Dolphin Emulator: Mario Kart Wii Highly Compressed
Ensure your game list is populated with your Mario Kart Wii ISO or WBFS file. Right-Click: Select Mario Kart Wii from the list. Choose the "Convert File" option from the menu
Save gigabytes of space on your PC, mobile device, or SD card. Mario Kart Wii Highly Compressed
Mario Kart Wii Highly Compressed: The Ultimate Space-Saving Guide