The planned Zuora release windows are:
Release Notes - Here is the link to the release notes. Changes are expected in Zuora Billing, Collect, and Central Platform (subject to change).
Release Status Updates - Any updates to the release status will be reflected in the comments to this post.
For the Sandbox and Production release schedule for the first half of 2022, see Zuora Release Management.
Here can we read more about how to use HTML Editor for billing documents?