Plesk, build constantly evolving software, which over time can become obsolete, giving way to a new major version. Below one can find the typical release lifecycle of any publicly available product.
Release / General availability - the new product is offered publicly, it receives bugfixes, new features, and updates on a regular basis, and technical support is offered through all available channels
Extended Support / End of Maintenance - The product stops receiving new features and bug fixes. Critical fixes, security updates, and technical support are still provided.
End-of-life (EOL) - Product development is ceased, and technical support is no longer offered.
Plesk recommends using the latest supported version of an operating system when deploying a new server because a server with a current OS has the longest potential lifetime before its OS Vendor Termination Date.
You can check the below article for a more detailed description of the Plesk Product Lifestyles: