how do I export the Canvas grades (grade book) to an excel?
In the current gradebook, there is an "Export" button in the upper left corner of the gradebook. That allows you to download the gradebook in CSV format which Excel can open. There is a complete description with screenshots at How do I download grades from the Gradebook?
If you are using the "new" gradebook there are instructions at How do I export grades in the New Gradebook?
Retrieving data ...