Hi,
Did this problem only appear recently?
How did you open the OneNote? From local app or from web?
Did you mean the OneNote slow or all Internet connection slow?
I suggest you check if this article's problem is related to yours:
Just checking in to see if the information was helpful. Please let us know if you would like further assistance.
If the response is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.