Hi TheTechyButterfly,
Thank you for posting here in the Microsoft Community Forum.
We understand that you’re having issues in OneNote, as you’re getting a message that says about signing into to OneNote to sync the notebook. Let’s check on this and help you in the best way we can to sort this out.
We appreciate you letting us know the steps you’ve already done so far on your end. Based on the information provided, this is more likely a conflict with your credentials or maybe a corrupted notebook. To know more about this, we’d like to ask the following:
- Does the prompt appear on a specific notebook only?
- Have you already tried signing into your account via OneNote Onlinefrom a browser to check if you’ll also get the prompt from there? If you haven’t done this yet, you may try to do so and confirm with us the result.
- How about deletingor clearing your credentials under Credential Manager? This would help to clear possible conflicts with the passwords saved under the Credential Manager. Please take note of your password for your account before doing
this action. You may follow these steps:
a. Type Credential Manager in the search box.
b. Under Windows Credentials > Generic Credentials, delete or remove all relating to
MicrosoftOffice2016.

c. Launch OneNote and provide your credentials, then check if you’ll still be prompted for the same message when you’ll open it again.
Please respond to this thread to let me know how the issue progresses. Similarly, if you have more questions, please inform me by replying to this post.