While you could always try PopOS i would expect the hardware and customization to Arch to perform better. Valve needed the best gaming performance and making games tends to require a similar or slightly higher performance then what playing will require.
For world building i can recommend obsidian as a good note taking app to connect dots and links between different files, there are some great tutorials about it. If you can afford it chatgpt plus can be mighty powerful as you can program a specific gpt for specific world building needs, a culture specialist, a character specialist, a storywritter, a dialogue and book generator,… each can hold multiple text files which it can reference from.
I am expecting game development to change a lot the coming years thanks to AI, i have seen some early experiments of ai generated animations. Personally i would keep things basic for a start and focus purely on game play and coding. Games and ideas change as you build on them and looks are most easy to change later.