how do I combine multiple projects as one to create one game?

I want to follow a tutorial that recreates games like color switch, frogger, line rider etc. But I want to combine them so that the complete game will have multiple mini games like the app 101-in-1 Games that have multiple games in one. Do I make separate projects then some how but them in one project? or do I make them all into one project but as different scenes? I want to be able to play each game that I create.

If you want to make sure there’s no conflict between classes, I would suggest you open every script of every project and put them in a separate namespace. Like :

namespace Frogger
{
    public class Foo : MonoBehaviour
    {
    }
}

Then, you can export every project whole assets to unity packages, and then merge everything in one.

One thing you may stumble upon, is conflicting Project Settings, like Inputs or Physics settings.

You’ll have to save those to custom assets, and reload them at runtime for each game. I believe there are extensions on the AssetStore for this.