I think this key cluster module [0] for the Ultimate Hacking Keyboard is pretty creative. I don't own a UHK or this module, but I think this is a better answer to your question than Workflowy, Notion, Roam Research, and pen and paper.
I just ordered a Moonlander, but the UHK was one of the boards I considered. Those interchangeable thumb modules are such a brilliant idea. If the UHK were ortho it would have been a much harder choice for me.