The Steamworks addon should actually be easier to use - you don't need a steam_appid.txt file and it includes all its dependencies so it should more or less just work after an export without extra configuration steps. The documentation is here so maybe double check that. If you are still doing extra configuration steps you used to do for Greenworks, make sure you stop doing them for Steamworks, as it might actually break it.
Thanks for the reply. I actually forgot to do that when I was testing the new plugin, so I don't think that's the issue... I'll keep tinkering a bit and update this if I find the issue.