Does anyone know, when comes final version FP 21??

Flash Player ships on a monthly schedule, typically aligned with Microsoft Patch Tuesday.  We ship one major version, followed by two patch releases, so we tend to increment a major version every 3 months.

The next release (Flash Player 21) is currently scheduled for early March.  In terms of our decision making, updating 2.5 billion users isn't easy.  Simply rushing fixes into the player often leads to problems that are worse than the thing we were originally trying to fix.  The major versions get the most exposure to the beta channel audience (several weeks vs. 1-2 for a patch release), so we tend to align risky fixes to the next major version to ensure both that the fix works, and that we didn't introduce side-effects that break other developers.