If you currently try to edit a OneNote notebook in Teams you are notified to use the OneNote web client. Of course you can also use your local OneNote client. This is caused by Microsofts throtteling measures for some Office 365 services to continue to meet excessive demand caused by Covid-19 crisis.
SharePoint Online services are also affected – expect to experience “strange” behaviour like new folders or files showing up for other users with delay.
For more details also see https://lnkd.in/dGJ85HP