Unity games with many games, like Roblox,Multi games with external program to launch games

Hello there,

It all begon with one game and many scenes. The problem with this approach is working with many students that are working on other games that we want to merge all of that in one game.
you can see the game live on technoviumunlimited.nl

Problem is that they work with other versions of unity and merging is hell.

We followed approach of Roblox, they launch the game from the browser and if there is id, then you can that game, otherwise they show kind of games list and then you can run that game from that list/overview.

I made c# script that is also opensourced on my github GitHub - technoviumunlimited/TechnoviumUnlimitedLauncher that checks if there is a new version of game, if so download and then you have option to click on play. After clicking on play, unity game launches and then you can play the game.

Now the question is how to build something similar like Roblox?

I was thinking to build like Roblox list of all games and if they want to play that game they click on play, if that game is not downloaded, then download it and run the game. But this takes a lot of time, like download and then launch the game. As I can see Roblox is much faster with launching and no need to download whole game.

So if someone can give me better idea then this?