Beau on notes
+1 for Obsidian. I heart MkDocs (rebuilt my hospital’s Internal Medicine handbook with it - vimbook.org), but also fell in love with Hugo. https://quartz.jzhao.xyz/ is a Hugo-based publishing tool for obsidian, supports all the essential features, super fast builds, and of course FOSS, self-hostable, GitHub Actions deployable, etc.
Like you, I’m still migrating many notes from elsewhere to .md files and Obsidian, so my own instance is rather bare (the reference website from the creator linked above is more complete), but here it is if you’re interested: notes.beauhilton.com
On iOS, “Working Copy” is an amazing Git app that plays nicely with GitHub and has a good markdown editor, so you don’t have to pay for the Obsidian app. I haven’t found an equivalent alternative on Android yet, just use GitHub web UI.