Got it. Do you want:
- A square on the PCB silkscreen around the header, or
- A square board outline, or
- A square/box in the schematic for grouping?
If you meant PCB silkscreen (most common for marking or pin-1 indication), here’s exactly what the Flux docs say:
“Silkscreen objects are ink traces used to identify test points, components, warning symbols, or any additional desired graphical element on your PCB
To add a silkscreen element:
- Left-click on the Layout object in the objects tree to ensure it's selected
- Right-click > Add > Silk Line / Silk Circle / Silk Rectangle”
Reply with which of the three you want, and I’ll tailor the next steps.