Change the aggregation function of Y-axis Series from Sum to Average in Google Sheets Bar Charts

I need to do something pretty basic: change the aggregation function "Series" (Y axis) of Sum to Average in a Google Sheets bar chart.

I see how to do it in the official documentation and in the graphics editor of the user interface in Personalize so Series so Aggregate Type.

However, every time I try to do it, there seems to be a technical problem. An error message appears saying

Unable to load the file

It is not that there is any file uploaded involved. This problem has persisted in all types of browsers and machines for 2 days.

I'm not sure what is the best way to make a reproducible example here that is not a link to one in Sheets (?).