Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hello Evan Draeger_CCB, Thanks for using Microsoft products and posting in the community. Regarding one of your users experiencing inability to access OneNote after changing their name and updating their AD and M365;
Your situation appears to be a business or organizational user with a permission error due to an AD domain or Microsoft 365 license change.
I suggest you go to the Microsoft 365 section of Microsoft Learn (English only) and post this issue, there are more users with similar issues as you and experts in this area who can give you more appropriate support:
Here is the link to the Microsoft 365 section:Microsoft 365 - Microsoft Q&A
Thank you very much for your prompt feedback, it was an honor to solve your problem. Best Regards,Arthur - MSFT | Microsoft Community Support Specialist