A family of Microsoft products that enable users to capture, organize, and reuse notes electronically.
Dear Capucine B,
Welcome to the Microsoft Community.
I understand that you are prompted with the 401 error message when using the Immersive Reader feature in the desktop version of OneNote, and I understand how you feel, I'm also a OneNote user.
According to your description, I also tried to use the Immersive Reader feature on desktop and the error message also occurred and my partner also encountered the same problem as yours. This could be a temporary server issue.
As we are not OneNote developers in the community, we can't be directly involved in the feature modification, but we have collected and feedback this issue to the development department and hopefully we can fix it soon.
In order to bring this issue to the attention of the development team as soon as possible, we encourage users to provide feedback through our feedback channel as well. Please click on the link:Ideas · Community (microsoft.com) (English platform) to post, where a dedicated developer will follow and comment on your feedback. You can share in this thread and I will vote this link.
While waiting for the development team to fix it, you can use the features in OneNote on the web side first.
I will also keep this thread open in the hope that more users will participate in the discussion. Let's gather more information.
Sorry for the inconvenience and thank you for your understanding and patience.
Best regards
Isabella-MSFT | Microsoft Community Support Specialist