Thanks for the replies.
After more tests, I managed to make the export work as long as I remove Steamworks, with webview and nw.js. The problem with NW.js seemed to come from command lines.
However, with Steamworks in the project, it still crashes all the time.
After even more tests, I noticed that keeping the Steamworks plugin in the project still works as long as I remove my events calling it. And my only events calling it are.
Steamworks is available --> set value to Steamworks.PersonaName
With that, the game works when launched OUTSIDE of Steam, but I still get an error message when trying to play it on Steam :
"An error happened while launching the game: game executable missing - C:\Program Files (x86)\Steam\(path)" (translated from French)
It's not an option to share the game publicly, as I worked on it for years, and I feel very uncomfortable just throwing my work out on the internet like that. However, if someone wants to take a look, I'd be happy to share it privately.