Although the Windows 10 November 2019 Update, version 1909, has been available since November 12, it’s been only available as an optional update for compatible devices.
However, starting December 6, if you’re running the version 1809 (October 2018 Update), then the feature update will now download and install automatically.
The reason is because, even though feature updates are no longer mandatory, devices nearing the end of service of a particular version will receive the most up-to-date version to continue receiving support and maintenance updates. (The Windows 10 November 2018 Update is in an 18 months lifecycle, and the end of support is scheduled for May 12, 2020.)
If you’re still on version 1809, the November 2019 Update is a very stable update as it is just version 1903, May 2019 Update, but with fixes, enhancements, and a few new features. You can learn more about the changes in this guide.
In the case that you’re still not ready, you can further block the installation using these instructions.