Whenever I opened OneNote 2016 or 2019, the error To sync this notebook, sign in to OneNote popped up. Normally I just click on the notification. Then I see the Sync icon next to the name of the notebook, and then everything works fine. Not very disturbing, but because it is mainly annoying I figured it out and described the solution below.
Solution for error To sync this notebook, sign in to OneNote
To be on the safe side, before following the step by step guide, make sure you know the username and password of how you are logged into OneNote. This can be a Microsoft account, or for example an account of your company. You need the user details to log in again later
How to fix error To sync this notebook, sign in to OneNote
Step 1: Open Credential Manager
Click Start, type credential, and click Credential Manager
Step 2: Backup credentials (optional)
As an optional step, you may want to back up the current cached credentials.
Click Windows Credentials
Then click Back up Credentials and follow the steps to save the credentials to a *.crd file, Again, this step is not required but may become handy.
Step 3: Locate the MicrosoftOffice16 credentials
In Credential Manager, click Windows Credentials
From there, scroll down to MicrosoftOffice16:ADAL:xxxxx
Step 4: Remove all MicrosoftOffice16_Data entries
Expand each MicrosoftOffice16_Data entry by clicking the downwards arrow.
Then click Remove to delete the cached user credential. Do this until all MicrosoftOffice16_Data entries are removed.
Step 5: Open OneNote 2016
Open OneNote. The error To sync this notebook, sign in to OneNote should not appear. You may have to sign in once again into your account, because you removed all cached credentials. However, in most cases, OneNote will just single sign on (SSO)