Before diving into the list, you need to understand the technical bottleneck. The Nintendo Wii was released in 2006. Its USB ports are (not 3.0/3.1), and they provide limited power. Crucially, the cIOS (custom IOS) that enables USB Loader GX to work—specifically d2x cIOS—has well-documented quirks with certain USB controller chips.
What's a good USB flash drive for USB Loader GX? : r/WiiHacks usb loader gx usb compatibility list
FAT32 is the universal standard. It allows you to run Wii games, GameCube games (via Nintendont), and homebrew apps all from one partition. USB Loader GX USB Compatibility List Report Review: