You see; you are in this category named game design support. Not game idea support.
There’s a HUGE difference between the two and I wish you to learn it (and everyone else that reads this). Please read THE WHOLE THING: https://en.wikipedia.org/wiki/Game_design, it is a 5-10 minutes read and it will help you for the rest of your Roblox career. If you stumble upon any issues, I have a thread which discusses some obstacles in game design.
Before anything else: Establish your values, purpose and etc. How you want to approach things to integrate your values within your products/services. And then lastly what you want to do.
I suggest you open up a document and start with the normal format; Game loop, progression loop and social loop.
If it’s just a place to utilize as a portfolio of sorts, then so be it. It doesn’t need to make money through the game itself. Showcase yourself with the game, post the game as a part of a portfolio post in #collaboration:portfolios and find work for others through that which would in turn net you money and potentially popularity.
A showcase isn’t meant to be a game with retention or money incentive directly in it. It should simply showcase your work.
To add to the solution, as @GeorgeOfAIITrades stated, its not really a “game” but more or less a portfolio showing what you are capable of doing. As visualization and an example, I have a music showcase that is made to represent a recording studio. This allows the user to explore the interior where the record labels hang throughout the halls. Each with their own description, title, etc. You click either a play/stop button to listen to each record. ( I should update it to just press the record or sign.)