Keynote data table

The object you have selected is a PDF file which is an image file, it is not a Keynote chart and can't be edited.

If you are certain a chart was placed on the slide, try reverting the file; go to: File > Revert to > Browse all versions

see this page from the User Guide which explains Revert:

Restore an earlier presentation version in Keynote on Mac – Apple Support (UK)

I don't understand how these is a mask applied to a chart on a Keynote slide

Can you post a screenshot showing the slide and this "mask"?

See the help page here: How to take a Screenshot on your Mac: Take a screenshot on your Mac – Apple Support (UK)

In the meantime as a work around, add a new slide, place a chart on the slide and change the data using the Edit Chart Data button.

As I understand you post, you have placed a chart on a slide and when clicking on the Edit Chart Data button the chart data table does not show?

Chart

Data Table



Good to hear you resolved the issue.

Out of personal interest, did you replace the image or use the Restore procedure?

Thanks for confirming