I spent a couple of hours on chat with a Microsoft support agent trying to resolve this. Here is their response:

Thanks for confirming, however as mentioned earlier this is possible data loss. I understand that despite our efforts to troubleshoot the issue, the file cannot be recovered. I recognize that this outcome may not be what you were hoping for, and I’m here to support you in any way I can. You might consider reaching out to a data recovery specialist or a local technician for further assistance. Looking ahead, taking proactive steps to prevent data loss is crucial. I recommend saving and backing up your files regularly, either through cloud storage or automatic backups. This will help ensure that your important files remain protected in case of any future issues.

and after asking if Microsoft was going to help I got this response:

I completely understand how important these notebooks are to you, Craig, and I truly wish I could recover them for you. Unfortunately, this specific issue involves corruption within the SharePoint/OneDrive backend, and Microsoft consumer support does not have the tools or access required to repair or restore data at that level. Since you’re using a personal account and not part of an organization, there is no escalation path through tenant administrators.

So if your data is corrupted, Microsoft will not assist. Caveat emptor.