The search for a "vnc server license key github" is a search born of confusion about the VNC ecosystem. The best solution is to stop searching for keys entirely and instead choose the right tool for the job from the start.
This path is simple, secure, supports the developers who maintain the software, and gives you access to updates and official support.
Disclaimer: This article does not encourage or provide methods for illegal software activation. All mentioned alternatives are open-source or legitimately free. If you'd like, I can: Show you to secure your VNC.
TigerVNC. It is actively maintained, audited for security, and has no license key requirement. It works on Linux, Windows, and macOS.