It is not a dichotomy - it is not all or nothing and it is not mutually exclusive - it is not "use composition always and never ever use inheritance".
Favor composition is just that your solution will most likely be better with it. There are still cases where you want inheritance but also most likely you don't want to create class hierarchy with 5 levels and everything inheriting form everything else but maybe have have a base class. So even in single application or microservice you might still have some inheritance and most likely more composition.
Besides composition uses interfaces heavily because you want to use DI with constructor injection and then you can switch implementation even at run time.
Favor composition is just that your solution will most likely be better with it. There are still cases where you want inheritance but also most likely you don't want to create class hierarchy with 5 levels and everything inheriting form everything else but maybe have have a base class. So even in single application or microservice you might still have some inheritance and most likely more composition.
Besides composition uses interfaces heavily because you want to use DI with constructor injection and then you can switch implementation even at run time.