Hi,
I read that it is not possible to enable feature to close steam after game exit.
So what i suggest is the possibility to watch one process. When this specific process will be finished, a simle kill -9 command can stop steam.
So i think that this should first wait that the process start, and only when the process is started, and so, lutris can start to watch if the process is finished or no.
For example, the user should complete a text area, to write which process to watch. (this one for exemple : Z:\home\powabanga.local\share\Steam\steamapps\common\rocketleague\Binaries\Win64\RocketLeague.exe ) lutris will wait that the process with this name start, and kill steam when it is stopped…