Installed version of OPC UA example cannot compile because it relies on the presence of Qt source code

Back in Qt 5, there were no pre-built libraries for "Qt for Automation"/"Qt M2M Protocols" (which Qt OPC UA was part of). Everyone had to build the libraries from source.

In Qt 6, this changed and commercial users can now install pre-built versions of the libraries.

Unfortunately, the installed version of the Simulation Server does not compile because it assumes that the Qt source code (including the bundled 3rd-party open62541 code) is always present: https://code.qt.io/cgit/qt/qtopcua.git/tree/examples/opcua/waterpump/simulationserver/simulationserver.pro?h=6.4.1

Workaround

Download the source code (either by checking out qtopcua.git, or by installing the Qt 5.15 Qt OPC UA source package from the commercial online installer) and load the example from the source tree.

Suggestion

Rewrite the Simulation Server to avoid depending directly on Qt sources and 3rd-party code.