After creating the secret in the settings, the video mentions "Back in the notebook you can now access the secret value [...]". However there's a caveat: At least for personal notebooks, the available secrets are only fetched once when the Secret() function is used for the first time since the notebook has been loaded. If any secret was created afterwards, the notebook has to be reloaded for the secret to become available.

That is correct. Thanks for the clarification, Fabian.