Installing .NET Framework 3.5 on Windows 11 may encounter error code 0x800F0950. This error usually means that a required file could not be found during installation from Windows Update or another location.
Here are a few ways to fix this problem:
Enable or disable tools using Windows features: In Windows settings, open the Start menu -> Settings (gear icon) -> Apps -> Apps and features -> "Optional features" on the right side -> ; Click "Add a Feature" -> Find ".NET Framework 3.5 (including .NET 2.0 and 3.0)" in the window -> Check this option -> Click the "Install" button.
Use Windows Update: Make sure your Windows 11 system is connected to the internet and try running Windows Update to get the latest updates and hotfixes. In Windows Settings, open the "Start" menu->Settings (gear icon)->Update and Security->click the "Check for Updates" button, and then wait for the system to automatically check and install available updates.
Using offline installer: If the above methods don't solve the problem, you can try installing using the offline installer. First, download the offline installer for .NET Framework 3.5 from the official Microsoft website. Then, run the downloaded installer and follow the prompts to install it.
Install using Command Prompt: Open Command Prompt (Admin Privileges) and run the following command:
DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:D:\sources\sxs
In the above command, "D:\sources\sxs" is the path of the Windows installation media. If you are using a different installation media path, modify the command accordingly.
If you have tried the above methods and still cannot solve the problem, it is recommended to refer to the official Microsoft documentation or contact the Microsoft support team for further help and guidance.