This often indicates a pending reboot. Ensure you restart the server, run sfc /scannow to check for system corruption, and try the installer again.
Open Registry Editor (regedit.exe) and navigate to: .net framework 4.8 offline installer for windows server 2016
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full
Look for a DWORD value named Release. For .NET Framework 4.8, the value should be 528040 or greater. This often indicates a pending reboot
Microsoft officially supports .NET 4.8 on Server 2016, but note: Server 2016 does not ship with 4.8 pre-installed (it comes with 4.6.2). The installer upgrades, not replaces, existing frameworks. All my legacy apps targeting 2.0, 3.5, and 4.x continued to work without modification. Open Registry Editor ( regedit
Warning: If your Server 2016 is missing the October 2018 servicing stack update (SSU) or later, the installer may fail silently. Always run Windows Update first before offline installing.