In the Confluence new editor, it's no longer possible to set any row or column to be a header. It was formerly possible in the legacy editor.
- Create a table in the Confluence new editor.
- Select a row or column in the middle of the table.
- Select Table Options drop-down and select Header Row or Header Column.
It's expected that the selected row or column would become the header.
The selected row or column does not get changed into a header, it only toggles the first row/column on and off.
No current workaround.