Looks like the current version of proplot does not work with matplotlib==3.6 (though it works fine with 3.5).
The import:
import proplot as pplt
Throws:
AttributeError: module 'matplotlib.cm' has no attribute 'cmap_d'
From: proplot/colors.py:3111,
_cmap_database = _init_cmap_database()
This might be fixable by changing the reference to cmap_d to point instead to matplotlib.colormaps.