From FreeCAD Documentation
- Select the component, optionally hide everything else to see better
- Draft Downgrade it. It will be exploded into a series of individual edges
- Start selecting the holes with Ctrl or by using Shift + B to box-select
- Press Draft Upgrade to turn back each hole into an individual wire
- Finally select all the remaining individual edges in the tree, which form the outline, and Draft Upgrade them
- Select Part → make Compound to join back all these wires into one object
- Select the compound and press the Arch Panel button