The problem is the QGLViewer. We do not include it in the QT5 Version, but we also do not have IFDEFs around all usages in the code. So either way we fix the cmake search scripts and adapt them to finding a proper qt5 QGLViewer or we look for all usages and put them into ifdefs.
The last part seems to be necessary either way, in case someone does not have QGLViewer installed.
File I got the error: cedar/auxiliaries/gui/Viewer.cpp Line: 149 But there may be more!