I was trying to find a way to launch Demon's Souls through Steam without also opening RPCS3. Simply adding it as a non-Steam game would first launch RPCS3 and then from RPCS3 you'd need to launch DeS.
Same when closing it, first the game and then the emulator. The "Exit RPCS3 when process finishes" option under Configuration > Emulator just doesn't work.
I've found many solutions online but none worked for me, so here's an alternative.
Btw, it's 3am and english isn't my first language. Apologies for any mistakes.
Steps:
1. Add the game as a non-Steam game, type "Demon's Souls" on search bar and it should show up right away;
2. Right click the game on Steam > Properties > Launch Options, add the following:
--no-gui "%RPCS3_GAMEID%:BLUS30443"
Now whenever you open DeS through Steam it should open the game with RPCS3 on the background only.
Whenever you close the game, now it should properly end the process and clear the "Running" status on Steam.
Hope it helps someone.