Agreed ownership of your notes is imperative. You do need some structure though. Try Logseq. I adopted Obsidian after Roam, but missed the low friction structure that Roam offered. But Roam was not secure and was proprietary. Logseq is the best of both worlds, is plain text based with minimal structure (markdown-ish) and is Git friendly. It's a work in progress, and needs a few files adding to .gitignore to minimise merge conflicts (pages-metadata.edn for one).