Sorry - which desktop file, is this 0ad.desktop in ~/.local/share/applications, or another (I can see a PrefersNonDefaultGPU=true line there, but no DRI_PRIME)?  Also, could you suggest any wrappers, then? Might be good to at least have some starting point.  

With the desktop file you already have a means, "DRI_PRIME=1 0ad", is probably what you need but that might depend on exact hardware or distribution. Look into prime and for older nivida into optimus. There are also plenty wrappers to tune for games.

Actually, yes, with the game started and a scenario loaded, I get a 0% usage for the dGPU from the System Monitor sensor if started from terminal, but not from the Application Launcher after adding the flag suggested above. which 0ad usr/bin/0ad which pyrogenesis usr/bin/pyrogenesis However, when run from terminal, both start the game, but as above - with 0% dGPU usage. If either of these is the "correct" exe to use, what to do, then, so the dGPU is used?

In French but nice and interesting video

Might be using the igpu then which would mean not nvidia  but should be enough to go to the ingame options an select the vulkan backend. Run "which 0ad" in terminal to get the path