This is not a good idea. I tried it, and while technically yes it works. It's just not worth it. Here are the steps you glanced over.
How to install SimCity 2000 on Steam from GOG.
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Download EXE from GOG
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Open the ~/.steam/steam/steamapps/compatdata/ so you can see which random ID the game is given
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Open Steam and add a new non-steam game
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Add the simcity2000 installer exe
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Go into the installer properties and set the game to use Steam Play/Proton
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Run the installer
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Go through the install process and get the new game's id. for me it was 3594652109
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Complete the install and exit
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Add the runner exe and the wine directory in the properties
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Save your changes and run the game.
In my case this didn't work, mostly because steam can't launch a DOSBox preconfig link while Lutris can. I am certain that if you installed SimCity 3000 or Ubisoft Connect it probably will.
Regardless still not a good idea. While this will get you the same effect as Lutris, it's much more involved and requires more conifguration. At least at this time. I hope Valve adds the functionality to install other games to Steam like in Lutris in the future as it will break down a lot of barriers. But as it is don't do it.