Hey there,
WeMod is not fully supported on the Steam Deck as of this time, at least with the SteamOS installed. We can’t really provide any assistance outside of a user-made thread here - My perfected and streamlined WeMod tutorial for Steam Deck
If it’s Windows, WeMod should scan and detect games from all drives, as it recognises games from my D: drive on my Steam Deck.
Hope this helps.