QTBUG-99656, except that the issue persists for static builds with the relocatable feature turned on, and more values seem to be affected.
ALL qmake variables that are not empty and start QT_* (except QT_VERSION) are affected, likely because of the extra bin in QT_INSTALL_PREFIX being propagated to the other values.
Build is not usable in Qt Creator due to the usual "Qt Version not installed properly" message. Interestingly the build is usable (at least from my one test) via the command line by using 'qt-cmake', though while the dependent build finishes successfully, the resultant lib binaries have not been tested.
The extra 'bin' is not simply always appended to the end. See attachments.
Configure command (with issue):