Correct way to handle 2 to 3 column switch

I'm using a NavigationSplitView on macOS which needs to show 2 or 3 columns depending on the selection of the sidebar.

Column 1 has a list of main activities. Some of these just have some data to show and some have a sublist.

Currently, when an item that has no sublist is selected, I set the 2nd column (content:) to:

Spacer()
    .navigationSplitViewColumnWidth(0)

This works, although it started hitting bugs requiring a workaround on macOS 26, which got me wondering, what is the correct approach here?

NavigationSplitViewVisibility.doubleColumn is not the solution, as this hides column 1, not column 2.