@hyeonshic , from the screenshot, it appears that map notes is .lpkx extension, i.e. it is a layer package.
What if you re-start the application and try to add layer package? If no, what is the source of the layer package, how it was created?
What if we change the location of this file to 'Desktop' or 'Downloads' from File Explored and then trying to add?
Thanks for your note.
I am following the directions in a tutorial book, "Understanding GIS: An ArcGIS Pro project workbook." So, I assume that the process directed in the book should work. Should I have done something differently?
@hyeonshic, I think issue is with the data, how was this file created?
If you created it, could you try re-creating?
I have tried what you suggested. But nothing resolved the error.