You couldn't just download iOS236. It wasn't on NUS (Nintendo Update Servers). You had to build it inside the Wii using the homebrew app. The app would take the clean, legitimate IOS36 from Nintendo, decrypt it in RAM, strip out its digital signature enforcement, patch the "ES_Identify" and "NAND" permissions, then re-encrypt and flash it into a new slot: IOS236.
: It is often the "first step" needed to install more advanced custom IOS files like , which are required to play games from a USB drive using USB Loader GX Stub Protection ios236 installer wii
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instead. Most modern homebrew apps no longer require IOS236 specifically, as they have been updated to use more modern custom IOS versions. You couldn't just download iOS236