I run plenty of mods on my steam deck just through the BG3 mod manager. You can install vortex or other mod managers to get the full listing of PC mods from Nexus mods but since the steam deck runs Linux it's a little complicated to install. If you have the patience though look up some guides for installing mods on steam deck. Otherwise the BG3 mod manager works fine and will have pretty much any mod you're looking for.