Not entirely sure if this can be self-hosted online, perhaps with VSCodium?
Foam is a personal knowledge management and sharing system inspired by Roam Research, built on Visual Studio Code and GitHub.
You can use Foam for organising your research, keeping re-discoverable notes, writing long-form content and, optionally, publishing it to the web.
Foam is free, open source, and extremely extensible to suit your personal workflow. You own the information you create with Foam, and you’re free to share it, and collaborate on it with anyone you want.