Did you try opening it from ArcGIS Pro (Open Project) as well as Windows Explorer (Double-click Project file)?
The error message is inaccurate in this case. Although there is no documented solution (from Esri) for this particular issue yet, a few workarounds attempted by people are given below (Please take backup before proceeding).
1. Close all the applications that are open. Please grant read/write access to the current user for the parent folder containing the Project directory. Try opening the project file.
2. From Window Explorer, right-click on the ArcGIS Pro Project File (*.aprx) > Click "Restore Previous Versions".
If any previous version is available, you may be able to restore it.
3. Copy the Project file to the default location (the default location, when you create a new project. e.g. C:\Users\...). Try opening the project file.
Think Location