What would be the usecase for those kwargs? Since they will be overridden afterwards anyways (i.e. Shadow(...., color="red") will not be red), it seems one should rather deprecate passing of kwargs.

Fair point. Actually, the properties for the shadow can be passed via prop, see e.g. https://matplotlib.org/devdocs/gallery/text_labels_and_annotations/demo_text_path.html; and they are not overridden.

I've now deprecated **kwargs. Could be debatable if we should deprecate prop instead and make **kwargs work, but **kwargs didn't do anything, so they are the easier deprecation.

This would now fit into #16096 (hence the particular deprecation comment). But I'll leave this standalone and merge the conflict in case anybody has different opinions on prop vs. `**kwargs'.

I think deprecating props and making kwargs work looks better (it's more consistent with basically all mpl APIs...) but won't insist on it either.

Actually, there's a suprising number of prop(s) parameters throughout the library. But I agree **kwargs would be the more common one.

Gone for deprecating props. Shadow is the only class that uses it in the constuctor and as attribute.

@anntzer Do you want to re-review because the content of the PR changed completely after your approval?