Undefined reference to functions in static library - c++

Question

I am building a lib that is wrapping a third party lib. Both the third party lib and the wrapper lib are build using cmake with the add_library function with the STATIC keyword. However when I try to build a executable that uses this wrapper lib, I get undefined references to the third party lib. Here is the code:
Third party lib spdlog.cmake:
include(FetchContent)
FetchContent_Declare(
spdlog
GIT_REPOSITORY https://github.com/gabime/spdlog.git
GIT_TAG v1.11.0
)
FetchContent_MakeAvailable(spdlog)
This lib can be build in different ways, but I have checked that we use the line add_library(spdlog STATIC ${SPDLOG_SRCS} ${SPDLOG_ALL_HEADERS})
Then the wrapper lib utils.cmake:
cmake_minimum_required (VERSION 3.1)
project (Utils)
# set C++20
set (CMAKE_CXX_STANDARD 20)
include(cmake/spdlog.cmake)
file(GLOB SRCS src/*.cpp)
file(GLOB HDRS include/*.h)
add_library(Utils STATIC ${SRCS} ${HDRS})
target_include_directories(Utils PUBLIC include)
target_link_libraries(Utils PRIVATE spdlog)
I link here using PRIVATE since we do not expose spdlog in the headers of this lib.
Then the executable cmake. Actually the wrapper lib is a separate project and the (static) lib that is created and its header files are is copied to a folder (Libs/Utils/lib and Libs/Utils/include) of the executable project.
cmake_minimum_required (VERSION 3.1)
project (Foo)
# Find Utils
set(UTILS_DIR "${PROJECT_SOURCE_DIR}/Libs/Utils")
set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${UTILS_DIR}/cmake/")
find_package(UTILS REQUIRED)
file(GLOB SRCS src/*.cpp)
add_executable(Foo ${SRCS})
target_include_directories(Foo PUBLIC ${UTILS_INCLUDE_DIRS})
target_link_libraries(Foo ${UTILS_LIBRARIES})
Finally the find script for the Utils lib:
SET(UTILS_DEFINITIONS ${UTILS_DEFINITIONS})
IF (UTILS_INCLUDE_DIR)
# Already in cache, be silent
SET(UTILS_FIND_QUIETLY TRUE)
ENDIF (UTILS_INCLUDE_DIR)
set(UTILS_INCLUDE_DIR
${UTILS_DIR}/include
)
set(UTILS_STATIC_LIBRARY
${UTILS_DIR}/lib/libUtils.a
)
include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(UTILS DEFAULT_MSG
UTILS_INCLUDE_DIR UTILS_STATIC_LIBRARY)
mark_as_advanced(UTILS_INCLUDE_DIR UTILS_STATIC_LIBRARY)
set(UTILS_LIBRARIES ${UTILS_STATIC_LIBRARY})
set(UTILS_INCLUDE_DIRS ${UTILS_INCLUDE_DIR})
The Utils lib builds fine, but when I build Foo, I get a lot of linker errors (the Logger.cpp is a file in Utils lib:
Logger.cpp:(.text+0x90): undefined reference to `spdlog::logger::sinks()
If I also copy the (static) lib of spdlog to libs folder and set UTILS_STATIC_LIBRARY to include this lib, it links. However since the spdlog is build statically I would assume that linking to the Utils lib would be enough.
Can somebody tell me what I am doing wrong?