Attempting to IMPORT matplotlib under Python 3.7.x on a Win10Pro results in error: "ImportError: DLL load failed: The specific module could not be found".
DLL name not given.
However, first importing PyQt5, and only then importing matplotlib works as it should.
Code for reproduction
install Python 3.7.x (tested both 3.7.2 and 3.7.3) on Win10Pro
install matplotlib (version 3.1.0) with pip - installs fine, no issues
install PyQt5 (version 5.12.2) with pip - installs fine, no issues
I don't understand the pyqt5 interaction. My guess is that you don't have Tk installed properly and the import fails when it tries to import Tk. Check your matplotlibrc and either clear the backend default or set it to Qt5Agg; its probably set to tk.