How to solve the error code 0x800f0831: Failed to install .NET Framework 3.5 in Windows Server 2016

There are several steps you can take to solve the error code 0x800f0831 when trying to install .NET Framework 3.5 in Windows Server 2016:

1. Check if .NET Framework 3.5 is already installed: Open the Control Panel and go to Programs and Features. Look for Microsoft .NET Framework 3.5 and check if it is already installed. If it is, you don't need to install it again.
2. Use the DISM command: Open Command Prompt as an administrator and type the following command: DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:D:\sources\sxs. Replace "D:" with the drive letter of your Windows Server 2016 installation media. This command will install .NET Framework 3.5 from the installation media.
3. Use the Windows Server 2016 installation media: Insert the Windows Server 2016 installation media and open File Explorer. Go to the Sources folder and find the file "sxs". Copy this file to your desktop or another location on your server. Open Command Prompt as an administrator and type the following command: Dism /online /enable-feature /featurename:NetFx3 /All /LimitAccess /Source:C:\sxs. Replace "C:" with the drive letter of the location where you copied the "sxs" file.
4. Check for Windows updates: Make sure your Windows Server 2016 is up to date with the latest updates. Go to Settings > Update & Security > Windows Update and check for updates. Install any available updates and try installing .NET Framework 3.5 again.
5. Disable antivirus software: Sometimes antivirus software can interfere with the installation of .NET Framework 3.5. Try disabling your antivirus software temporarily and then try installing .NET Framework 3.5 again.