When building Pyside with the following command line:
PySide2 is built and installed to pyside3_install, however the PySide2 support module which provides the PySide2 _feature_ support is not installed there.
It appears that this is only installed in the creation of the wheel, which I do not perform due to the specifics of how we install PySide2 in a Python installation that is embedded in an application (Autodesk Maya).
Manually copying the PySide2/support module into the site-packages/PySide2 dir during the packaging process corrected the issue, but I think the fix really needs to occur inside the PySide2 build process.
When starting the application with embedded Python interpreter, and PySide2 is imported, the following message is shown:
Qt 5.15.1 (Python 2): _feature_ could not be imported when starting maya/mayabatch.
- Start Maya or mayabatch with Qt 5.15.1
Result: A following error is returned: