You can easily duplicate an existing project by selecting it in the Project Explorer panel, using either the right-click contextual menu or the corresponding keyboard shortcuts (Ctrl+C and Ctrl+V).
However, it is required to perform an additional step in order to continue to have the Project Explorer panel refreshed correctly for the new project: right-click on the target project and select the "Properties" option. The properties dialog box will open, select the "C/C++ Build" item in the property tree, then the "Refresh Policy" tab. For each required build configuration (e.g. "Debug", "Release", etc.), change the resource by deleting the old project and adding the new one.
Failure to do so will result in strange behaviors: a common problem is the inability to flash a firmware because the binary firmware is considered as "missing", while it is indeed present in the output directory, but has just not been refreshed into the Project Explorer panel.