Hi! I've also been playing Roblox since 2009, and I know the struggle of wanting to create an "original" game that hasn't been made before on Roblox.
As a member of RAT and a fan of Polymorphic's games in that group, I just wanna say that the games you were a part of (and others, I'm sure) are amazing.
As for original games, that's unfortunately pretty difficult because Roblox Studio and the Roblox platform has some limitations as to what games you can create. However, I can still offer some ideas that I've always wanted to make, but couldn't because of my lack of scripting/building ability.
I used to be a huge fan of Pokemon, and games like Pokemon Arena X on Roblox. I've always wanted to make a game based off Pokemon, except instead of being limited to using 6 Pokemon at a time, I'd want to be able to build an army. For example, I want to be able to fight other trainers by commanding and summoning my various groups of Pokemon while flying on my Dragonite. Or having a separate cutscene when you encounter another trainer that looks something like Warlords 2: Rise of Demons (search this up on Google and you'll be able to see the format I'm talking about for a fight scene). If not a Pokemon conquest, maybe just another Pokemon minigame; those were always popular but ended up being deleted for reasons I'm not 100% sure of.
I've also always loved action games. What about making a game where you kill other Robloxians, but in order to do so, you have to possess NPCs within the game? You're a spirit with no power except the a starterpack of a few weapons and the ability to take over NPC bodies or characters, ranging from a snail that is extremely slow to someone who owns a gun or tank or whatever. I've never really thought about the details, but you can only possess a character for a certain amount of time before they realize they're being possessed and expel you. Then to switch "bodies", you have to spin a wheel or something and you can integrate game passes to improve probability.
These are just some ideas that you definitely don't even need to consider, and may not even be possible to integrate on Roblox's platform. But feel free to respond with your feedback or even add me on Roblox if you want to collaborate more. Just respond with your wishes and I'll get back to you when I come onto Brainly again.
Hope I was able to help :)