Hi David,
Thanks for posting in the community. We are happy to help you.
Per your description, I would like to collect more information to troubleshoot.
Generally, the "Paste link" option is available when copying an Excel chart object, but not available when copying an image file. For the chart you copied, I would like to know if it is an Excel chart or an image file. For example, if you save an Excel chart as a picture to your device, and then insert the image file into an Excel workbook. Although the inserted image looks like an Excel chart, it is not an Excel chart object, and the "Paste link" option will be grayed out in PowerPoint.
Also, to verify this, you can create a new Excel chart via the Insert tab> the chart option in the Charts group, such as Column, and then copy the real Excel chart and check the options in the Paste Special dialog in PowerPoint.
If the option is still grayed out when you copy the newly created Excel chart, please point it out and let us know. We will keep on assisting you.
We look forward to your response. Thanks for your cooperation.
Sincerely,
George | Microsoft Community Moderator