This topic at the moment is not able to be confirmed and referenced with proper material, and likely wont be until the war concludes and things are documented, like with wars in the past. The New York Post is a more sensationalist news outlet, and oftentimes panders to myths and misinformation, yet the information in this one seems to be at least grounded in reality, with it referencing a New York Times article, where they were told by "Unnamed Officials" that Russia's launch on November 21st last year of a conventionally armed ICBM was planned before the United States greenlit missile attacks deeper into Russian territory. Because of the anonymous nature of it and the lack of credible resources to confirm this, it can't be reliably proven yet.
As with everything in this war, propaganda and misinformation are prominent, and it must be considered with this.