Just summary build steps.
First, you need to install these packages: qt5-default, qtchooser, qt5-qmake, appmenu-qt5, qtdeclarative5-dev, qttools5-dev, qttools5-dev-tools, libqt5x11extras5-dev, libglib2.0-dev, libgio2.0-cil-dev, libfm-dev, libmenu-cache-dev
Then clone pcmanfm-qt from https://github.com/lxde/pcmanfm-qt
Enter pcmanfm-qt directory, type: cmake -G “Unix Makefiles”, then run: make && make install
After installation, you need to add a file “x86_64-linux-gnu-local.conf” in /etc/ld.so.conf.d and put “/usr/local/lib/x86_64-linux-gnu/” in it. Run sudo ldconfig to make the setting available.