The SHX font format is not documented nor supported by many libraries/packages like Matplotlib and Qt, therefore only SHX fonts which have corresponding TTF-fonts can be rendered by these backends. The mapping from/to SHX/TTF fonts is hard coded in the source code file: fonts.py
Since ezdxf v1.1 is the rendering of SHX fonts supported if the path to these fonts is added to the support_dirs in the config_files.
If you wanna use new installed fonts which are not included in the current cache file of ezdxf you have to rebuild the cache file:
import ezdxf
from ezdxf.fonts import fonts
fonts.build_system_font_cache()or call the ezdxf launcher to do that:
ezdxf --fonts