OneNote for Windows 10 goes read only on October 14.

The pre-installed OneNote in Windows **10** is going away, starting with going read only from October 14.

ESU won't help you either.

https://www.theregister.com/2025/08/22/the_support_clock_counts_down/

Move your stuff to "OneNote on Windows"

https://support.microsoft.com/en-us/office/moving-to-onenote-on-windows-4ba7b498-aafc-44b1-8326-a582a6c71196