In short, in my opinion:

- Encapsulation / interfaces is a good idea, a continuation of the earlier ideas of structured programming.

- Mutable state strewn uncontrollably everywhere is bad idea, even in a single-threaded case.

- Inheritance-based polymorphism is painful, both in the multiple (C++) and single (Java) inheritance cases. Composable interfaces / traits / typeclasses without overriding methods are logically and much more useful.

Over multiple decades, I have come to reject all of it! Even interfaces.

I watched over and over again people writing code to interfaces, particularly due to Spring, and then none of those interface ever got a second implementation done and were never, ever going to! It was a total waste of time, even for testing it was almost a total waste of time, but I guess writing stubbed test classes that could pretend to return data from a queue or a database was somewhat useful. The thing is, there were easier ways to achieve that.