I'm not saying you can't do multi-threading or concurrency in C++. The problem is that it's far too easy to get data races or deadlocks by making subtle syntactical mistakes that the compiler doesn't catch. pthreads does nothing to help with that.
If you don't need to share any data across threads then sure, everything is easy, but I've never seen such a simple use case in my entire professional career.
All these people talking about "C++ is easy, just don't use pointers!" must be writing the easiest applications of all time and also producing code that's so inefficient they'd probably get performance gains by switching to Python.