I imported an OPML into Omni Outliner. I converted it into OO’s native format, but there is still a stubborn “Topic” row that I can not delete (see the attached image). This row does not exist if I create a new outline from scratch.
It does look like a data row, doesn’t it ?
It’s the column header label – not a data row, so not ‘deletable’, but you do have a choice of whether or not to display it:
View > Column Headers > Hide