To build LXQt, the following steps are recommended:
First, build the whole Xorg Chapter, including Wayland support with required and recommended dependencies. Test that the environment works with twm as the window manager. With experience, some of the packages can be omitted, but that is not recommended for first time users.
Second, build the required parts of Qt. The full package, Qt-5.15.12 is quite long and has a lot of dependencies. As an alternative, the required components needed for LXQt can be built using the procedures in qt-alternate-5.15.12.
Finally build the LXQt desktop using the pages below in order. The packages in the applications section are optional, but as a minimum, qterminal-1.4.0 is recommended.