Hello there,
Might be an temporary issue with Onedrive.
Are you able to open projects stored locally?
There is indeed a backup feature in MS Project. To use this feature, open or create a project and then click File > Save As. In the lower side of the "Save As" dialog, click the little Tools pick list button and select the "General Options" item. In the "Save Options" dialog, you will see the "Always Create Backup" option. If you select this option, every time you save a project, it will save as second copy as a backup (BAK file) in the same location as your MPP file.
The below thread discusses the same issue and you can try out some troubleshooting steps from this and see if that helps you to sort the Issue.
Hope this resolves your Query !!
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