I don’t think it’s a bug. What the nvidia-offload script does is set some environment variables. Using it inside the steam command override probably doesn’t work because steam is in a special sandbox, it likely just fails to run the script correctly.
Have you tried starting steam itself with nvidia-offload? That should propagate the variables correctly for steam games to then pick them up.
If you assert that works, we can either make it permanent by editing the steam desktop file, or set the environment variables directly in all your steam command overrides if you really want to run steam on the iGPU (very reasonable desire if you’d like to use big picture mode).
Also, props, I think you’re the first person I’ve seen with a reasonable nvidia config. Note that finegrained probably doesn’t actually work at the moment though: Nvidia never suspends - #2 by TLATER