@deadcream Thank you, that was it: “Keep launchers separate” checkbox in “Behaviour”.

Note: That option is normally (depending on “Sort” order) grayed out and cannot be changed.

So:
- Switch “Sort” to “Manual” (this un-grays the checkbox)
- Un-check “Keep launchers separate” checkbox.
- Switch back to your favourite “Sort” - e.g. “By desktop” (this re-grays the checkbox, but now it’s un-checked).