You added a plugin declaration to MyCompany/MyModule/etc/di.xml:
What will be the effect of this declaration?
A. An exception because plugins must not be applied to the interfaces
B. An exception because of the syntax error in the declaration
C. The plugin will be ignored because ActionInterface will never be instantiated directly
D. The plugin will be applied to all implementors of the ActionInterface
Answer: D
I agree with D as the limitation for plugins does not include interfaces.
https://devdocs.magento.com/guides/v2.4/extension-dev-guide/plugins.html#limitations
Correct answer is D
https://stackoverflow.com/questions/62734221/magento2-writing-plugins-for-interface