Everything you write can leave the app in a standard format. Export is part of the Sync, Pro and Lifetime plans.
One note
Open the note menu and choose Export: Markdown keeps the structure for another app, HTML keeps the formatting for the web, PDF is for sending to somebody who just needs to read it. On mobile the export hands off to the share sheet, so it can go straight to mail or files.
The whole library
Open Settings, go to the Data tab and choose Export All Notes. You get a single ZIP of Markdown files with your folder structure recreated as directories, which any other app can read. Locked notes are skipped, and the app tells you how many; unlock one and export it on its own from the note menu.
Why this matters
The underlying database is a file on your disk on every plan, and on a paid plan export turns it into files any other app can read. There is no version of this where your writing is stuck inside an app you no longer want to use.