Problem not knowing " QT += gui-private " in Qt

[saeed]

Hi all,
I have a lib that run correct when open with CMake but when I open lib with *.pro program has error.
When I enter this " QT += gui-private " in *.pro for a project, the program gives the following error. I use Qt 6.0.1 GCC 10.3.1 in Ubuntu 20.04
-1: error: cannot find -lxkbcommon
-1: error: collect2: error: ld returned 1 exit status
-1: error: [Makefile:321: untitled6] Error 1

[saeed]

I install " libxkbcommon-dev " and fixed error