Not sure you miss much not having the Intel GPU available, though.
If it’s the one “build into” the CPU, it’s weak enough that the overhead tends to hide the benefits. And you’d have to configure darktable to assign a GPU or the CPU to each pipe (e.g. you can’t use both GPUs for the export pipe…)
You could perhaps check if the appimage acutally uses both GPUs.
This configuration (iGPU and GPU) is in my laptop.
Normally I don’t need iGPU, but my main GPU this is eGPU and sometimes (e.g. durig vacations) i have only iGPU.