Would you please confirm: What is the Operating System you are currently using for the installation?
I have tested in my SharePoint Server 2019 farm and the components are installed successfully, so there should be nothing wrong on the server side.
According to the error logs, it is the “.NET 3.5 for Windows 8” that fails to install during this process.
Please check if you have enabled “.NET Framework 3.5” via Server Manager (for Windows Server) > Features > .NET Framework 3.5 (includes .NET 2.0 and 3.0).
Make sure the features are properly installed and then reboot your machine. After that, try to install Workflow Manager 1.0 Refresh (CU2) again.
You can refer to the document here for how to enable “.NET Framework 3.5” on other OS: How to enable the .NET Framework 3.5 by using Control Panel in Windows 10 and Windows Server 2016.
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