You should only create and use WBFS files compiled from physical Wii discs that you legally own. Downloading game files from third-party ROM sites violates copyright regulations and poses a risk of malware.
Here’s an informational article based on your search for — aimed at users interested in playing the game via USB loaders on a modded Wii console. wii fit plus wbfs
actually contains much less data; a WBFS file "scrubs" the empty space, typically bringing the size down to around 0.6 GB to 2 GB depending on the region. USB Loader Compatibility : Popular homebrew apps like USB Loader GX You should only create and use WBFS files