The .cab version does not match your server’s image. Solution: The "new" cab you downloaded may be for a different build (e.g., Server 2016, or a different cumulative update level). Extract the .cab from a Windows Server 2012 R2 ISO with the same Service Pack or update level as your running server.
If you want, I can:
reg query "HKLM\SOFTWARE\Microsoft\NET Framework Setup\NDP\v3.5" /v Install If you want, I can: reg query "HKLM\SOFTWARE\Microsoft\NET
Instead, locate your original Windows Server 2012 R2 installation media (ISO). The file on that media remains the definitive, digitally signed, and safe version. Use modern deployment tools (DISM, PowerShell) to install from that source—this is the fastest, most reliable, and secure method in any environment, new or legacy. You can install
You can install .NET 3.5 using either the graphical interface or the command line. Method 1: Using Server Manager (GUI) Install Net Framework 3.5 SP1 Offline on Server 2012 R2 If you want