I finally manage to put my Nvidia as primary GPU, with , we got
several references on internet  and I'd check as mint and ubuntu
have prime-select nvidia  tool, to do this automatically, I guess.
I think we could improve our wiki page Howto/NVIDIA and Howto/Optimus
xrandr --setprovideroutputsource modesetting NVIDIA-G0
and the attached file
Sérgio M. B.