Stardew Valley

I did it, but it's been long enough now that I can't remember what I did.

Why do you want to do this?

If you want to be able to play unmodded but still with SMAPI then the Stardrop mod manager is the answer.

You can have seperate profiles where you can choose which mods to load for which profile, so you could have one for single player with all of them loaded, another where they are all unloaded and one for multiplayer with only some loaded for example.

If you really want seperate unmodded and modded installs, we aren't sure how to help but hope that you can find a solution!

Though the easiest might be one on steam and one from gog if you want truly seperate installs.