Write CMake file for project that using GTKMM and An include library

Code
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Hello,
I am trying to write a CMake file for my project, this is the project tree :

Project
 I CMakeLists.txt
 I___src
 I-----I__main.cpp
 I-----I__window.cpp
 I-----I__windows.hpp
 I-----I__operations.cpp
 I-----I__CMakeLists.txt
 I
 I___incld
 I-----I__tinyexpr.c
 I-----I__tinyexpr.h

So now i am ge want to link the tinyexpr.h to the program, with g++ i know how to to it but with CMake it’s myFirst time,
This is the CMakeLists.txt of project:

cmake_minimum_required(VERSION 3.20) 
project(MCalc) 
set(CMAKE_CXX_STANDARD 20)
 find_package(PkgConfig) pkg_check_modules(gtkmm gtkmm-4.0)
 add_subdirectory(src incld)

And this is the CMakeLists.txt of the src directory:
link_directories(${GTKMM_LIBRARY_DIRS} ${INCLD}) find_package(PkgConfig REQUIRED) pkg_check_modules(gtkmm REQUIRED IMPORTED_TARGET gtkmm-4.0 glibmm-2.68) set(SOURCES main.cpp operations.cpp window.cpp ${INCLD/tinyexpr.h}) add_executable(MCalc ${SOURCES}) target_link_libraries(MCalc PkgConfig::gtkmm)

So if any one could help to make this CMakeFiles work with my program i would be really happy.