Can I export my notes, or am I locked in?

You can export everything at any time, generated entirely on your device: Markdown files in a zip with attachments included, a full JSON backup, or self-contained HTML - per note or for the whole account.

Import works too: bring notes in from Obsidian, Apple Notes, Google Keep, Standard Notes, Simplenote, and Samsung Notes. Lock-in is not part of the business model.