I have no idea if this is necessary

source/Irrlicht/CMakeLists.txt

@@ -341,6 +341,11 @@ add_library(IRRMESHOBJ OBJECT
 	${IRRMESHLOADER}
 )
 
+target_link_libraries(IRRMESHOBJ
+  PRIVATE
+    json
+)
+
 add_library(IRROBJ OBJECT
 	CBillboardSceneNode.cpp
 	CCameraSceneNode.cpp