Hi, please check the location from the .exe file, you want to start. I had the problem, that the path is not set right if in the path are spaces. Then the installer do take the rest after the spaced path, also after the spaces to the startoption. You can copy this and past it to the (i know just the german word) "Ziel" path and put it together.
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Add a non-Steam game does not works with Proton (all release) - I have an error message : "Failed to launch Game_Name" Please link any large code pastes as a Github Gist
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