How do I format report records based on a checkbox value?

I have an attendance report that I am trying to format with styles. I have done conditional formatting before in Creator, but this is not working.

I have a single choice checkbox field in my form that I want to use as the criteria for the formatting. If the "Attended Today" field box is checked, I want to highlight the record green.

I cannot see the field name in the choice list to trigger the formatting when I choose "Selected Records". Can checkbox fields be used?? If not, what can I use?

What even defines whether a field appears as a choice to trigger formatting? There are numerous other fields that don't show as choices (even though they are irrelevant for this use) and I don't know what makes them chooseable or not. Can't find it in the knowledge base.

This should be simple, but I cannot make it work!