The corrplot function was deprecated in new seaborn. You have to now call the function from another module.

corrplot.py

from seaborn.linearmodels import corrplot

sns.set(style="darkgrid")

f, ax = plt.subplots(figsize=(9,9))

corrplot(df_imputed,
            annot=True,
            sig_stars=True,
            cmap=cmap,
            ax=ax)

f.tight_layout()