I've recently come across the pay-to-use Roam Research (https://roamresearch.com), here a nice introductory video (https://www.youtube.com/watch?v=yMiodsp6OKo) and Obsidian (https://obsidian.md) which is similar, but available as a desktop app, and is free for personal use
These are basically graph based personal wikis (with backlinks) based on markdown with outlining features and graph generation to show an information overview or relationships between nodes.