ребята неосилили cmake + ninja
потому и пишут гупые отмазки типа:
What is the correct way to use threads (such as pthreads)?

thread_dep = dependency('threads')

This will set up everything on your behalf. People coming from Autotools or CMake want to do this by looking for libpthread.so manually. Don't do that, it has tricky corner cases especially when cross compiling.

а делов-то:
https://stackoverflow.com/questions/33991918/link-to-pthread...

set(THREADS_PREFER_PTHREAD_FLAG ON)
find_package(Threads REQUIRED)
target_link_libraries(my_app threads::Threads)