‘Offline’ is currently the default which is explained in the source code:
“This is the scenario for the “offline” rollout. Firefox Suggest suggestions are enabled by default. Search strings and matching keywords are not included in related telemetry. The onboarding dialog is not shown.”
Switching to ‘online’ would trigger a dialog that comes up when you start the browser. Only clicking ‘Allow suggestions’ on the dialog would opt you into the search query collection.