Here’s the official guide for importing OneNote notebooks. And yes, you don’t need any paid accounts, only basic access to your notebooks
Importing and exporting | Joplin
Importing from OneNote
Joplin can also import OneNote notebooks. To do this:
Visit OneNote Web.
Right-click the desired notebook and choose Export notebook.
Follow the instructions to download the backup. It should be a ZIP file.
Open the desktop application and go to File > Import > ZIP - OneNote Notebook, and select the exported file.
For other guides you may refer to community compiled list