Dear Dorothy Ng,
Greetings! Thank you for posting in Microsoft Community.
As per your description, you get notifications on PowerPoint and the file is failed to upload to OneDrive.
I'd like to help you, please let us cooperate and please don’t worry, we can work together to narrow down and resolve the situation.
May I know how do you upload PowerPoint file to OneDrive?
By using PowerPoint for Mac application, click Save button, choose OneDrive as location and click Save?
If yes, you may try following steps and check if the same notification still appears. It helps you check if the issue only happens in PowerPoint desktop application.
1.Firstly, save the PowerPoint file on your Mac, such as Desktop.
2.Then go to OneDrive on the web in browser, click the Upload button, upload the PowerPoint file.
And to better help you and narrow down the issue, I'd like to collect following information:
1.Does the issue happen when you upload a specific PowerPoint file to OneDrive? If you try a different file, does it work?
2.Are you using OneDrive for business or personal OneDrive?
3.May I know your PowerPoint application version?
Thanks for your time and cooperation! We hope you stay safe and healthy always.
Sincerely,
Tina | Microsoft Community Moderator