If anyone happens to be playing on Steam Deck (or any Linux desktop), the launch options are slightly different:
DX11 no launcher: –skip-launcher
Vulkan no launcher: bash -c ‘exec “${@/bin/bg3.exe}”’ – %command% --skip-launcher
Though for this particular title, the Vulkan one is really crashy on my system rn, which is ironic since the DX11 shaders are converted to Vulkan on Linux.