Not sure if there is a question here.
Certainly on optimus machines when using the performance profile rendering is done thru the nvidia adapter, display is always thru Intel (on most optimus machines.
With the on-demand profile the nvidia adapter is only used when specifically ‘told’ to. I gather this can be done via an env or command, or with gnome-shell thru the context menu option to use dedicated …
To what advantage there is with that context menu option to open an app is debatable, would depend on the app. For most normal apps there isn’t any.
I don’t have any games, that would be an area to see how it works.
As far as media/video players only mpv can take full advantage of this, i.e using nvdec or for some vdpau for decoding if set up for vdpau in mpv.conf.
Vlc and others cannot. Whether the vlc gui window is rendered by nvidia is off no value, I’ve no idea how to tell anyway…