> So people started writing stupid unit tests for getters and setters in Java DTOs to reach the goal

Ideally, the code coverage tool would have heuristics to detect trivial getter/setter methods, and filter them out, so adding tests for them won't improve code coverage. Non-trivial getters/setters (where there is some actual non-trivial logic involved) shouldn't be filtered, since they should be tested.

Although, there is room for debate about what counts as trivial. Obviously this is trivial:

    public void setUser(User user) {
       this.user = user;
    }

But should this count as trivial too?

    public void setUser(User user) {
       this.user = Objects.requireNonNull(user);
    }

Probably. What about this?

    public void setOwners(List<User> owners) {
       this.owners = List.copyOf(owners);
    }

Probably that too. Which suggests, maybe, there ought to be a configurable list of methods, whose presence is ignored when determining whether a getter/setter is trivial or not.