How to enable .NET Framework 3.5 on Windows Server 2019
I. Using Command Prompt
1. Run Command Prompt as Administrator
2. Execute the following command
DISM /Online /Enable-Feature /FeatureName:NetFx3 /All
An alternative option is to use the Server Manager software that was originally used to install and setup the server. Ensure that your account has administrative privileges before proceeding.
II. Using Server Manager
1. First you need to open the Server Manager on the system where you want to install the .NET Framework 3.5.
2. In the Server Manager, open the “Add Roles and Features” Wizard by clicking Manage –> Add Roles and Features.
3. Step forward to “Installation Type” and select “Role-based or feature-based installation”
4. Select the destination server for installation.
5. Click on “Features” and select the sub-feature ” .NET Framework 3.5 (includes 2.0 and 3.0)” under .NET Framework 3.5 Features.
6. Now, we get to the “Confirmation” step. Click “Install” to begin the installation.
7. Installation should have now succeed.