mosquitto provides CMake targets:

  find_package(unofficial-mosquitto CONFIG REQUIRED)
  # C bindings
  target_link_libraries(main PRIVATE unofficial::mosquitto::mosquitto)
  # C++ bindings
  target_link_libraries(main PRIVATE unofficial::mosquitto::mosquittopp)

mosquitto provides pkg-config modules:

  # mosquitto MQTT library (C bindings)
  libmosquitto

  # mosquitto MQTT library (C++ bindings)
  libmosquittopp