Access Steam features in the Windows WebView2 exporter. Requires r359+.
You should probably have a debug text saying "Steamworks is available/not available" depending on if Steamworks works or not.
It will help on understanding why it doesn't work. It might be you're not using the right compatible files.
I haven't tried yet the Steamworks for Webview2 plugin so I don't know yet about the plugin.
But in the meantime, I wrote a tutorial on my blog on how to export to Steam with NW.js and which versions of files to use to get your game working on all platforms (Windows, Mac, Linux, and Steamdeck) if you want.
The article is here: sleepingpanda.games/blog/how-to-export-your-construct-3-game-for-steam-and-steamdeck
Hope it helps!