Steam linking

I want to link a non-Steam version to my steam account. But the Popup when first starting Star Conflict from my Steam-App did not show so I could not import my nonSteam Account, need help since I already spend money on the non steam account and really would like to transform it to the steam version. Since you have a native linux client I wonder why steam installed via proton where do I get the native linux client the download button on the webpage redirects directly to .exe file
regards Chris

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