From the documentation (https://code.visualstudio.com/docs/getstarted/telemetry ) it seems there is a supported way to completely turn off telemetry. Is there something else in VSCode that doesn't respect this setting?
> extensions may be collecting their own usage data and are not controlled by the telemetry.telemetryLevel setting. Consult the specific extension's documentation to learn about its telemetry reporting and whether it can be disabled.
They must have reintroduced the telemetry setting. I can't remember if I deleted the old one, but my setting on that new value was set to "all" by default.