Drop down boxes in Object Export Options not active for images

The drop down options in my Object Export Options dialog box in InDesign 16.0 for Mac stopped being active for images today. I've been been adding tags to things today, but the options are inactive for any image whether it's tagged or not. See screen shot. The options are active for objects other than images. Any ideas why that would be? I want to make some of the images Artifacts so they are not recognized in my PDFs for text to speech conversion.  

Many thanks