Notion has worked okay for us in the past, but recently we’ve moved to just using markdown documents in Git. It’s just as searchable, and stays closer to the code. RFCs et al. are submitted as PRs.
I can heartily recommend Obsidian[0] as a way to augment "markdown documents in Git". It lets you cross-reference between your markdown documents using [[wiki links]] so you can start building a knowledge graph.
