Text Field Properties Borders and Fills area choices are greyed out

I have a large document with many fields, where a client wants a few fields to be highlighted in the background. Under "Text Field Properties > Appearance" the Borders and Fills are greyed out, but the Text area works. I see in this post: https://community.adobe.com/t5/acrobat/text-field-properties-will-not-allow-me-to-add-a-border/m-p/9482032#M77344 there was a fix three years ago, but this is 2021. 

I'm on MacOS Catalina, using the latest version of Acrobat DC.