Welcome to the community. 
WeMod does not officially support Steam Deck. WeMod provides cheating services for PC.
Steam Deck is a Linux-based operating system. Whereas WeMod is developed for Windows operating systems.
There is an unofficial, third-party guide to getting WeMod to potentially work on your Steam Deck, which you can find easily by using the search tool before posting. Here you go: My perfected and streamlined WeMod tutorial for Steam Deck.
Note this is a third-party guide. WeMod itself cannot provide assistance for operating systems it does not officially support.
Have a pleasant day.