The app you're looking for is Obsidian. Notion abandoned that goal years ago. Notion is making money for being a project management / team wiki. They don't care personal note taking.
"Notes and Domino is a cross-platform, distributed document-oriented NoSQL database and messaging framework and rapid application development environment that includes pre-built applications like email, calendar, etc." [0]
Lotus Notes was the original offline-first everything app, including cutting edge PKI and encryption. It worked over dial-up and needed only a handful of MBs of memory (before the Java rewrite at least). Has anything else really come close since?
I do writing with RAG and it can be implemented to suprisingly good if you already have your own writing that the text is being generated from. FAQs etc can be pretty easy when your content is context for the AI.
After a few rounds of AI generating AI content from AI content, I'm sure it could eventually become slop...like the model collapse lol idk.