The issue here is the incorrect @Builder annotation on the parent class. The documentation for @SuperBuilder mentions:

Most importantly, it requires that all superclasses also have the @SuperBuilder annotation.

So the correct parent class would be:

@Data
@SuperBuilder     // <- annotation replaced here
@NoArgsConstructor
@AllArgsConstructor
@EqualsAndHashCode
public class Party {

    protected Long id;
    protected String status;
}

Addendum:

A key difference between both annotations is that @SuperBuilder also creates a constructor of the class expecting a corresponding builder argument.

For Party it would look like:

protected Party(PartyBuilder<?, ?> b) {
    this.id = b.id;
    this.status = b.status;
}

and for Person:

protected Person(PersonBuilder<?, ?> b) {
    super(b);
    this.name = b.name;
    this.sex = b.sex;
}

As you can see, the child class constructor wants to pass its own builder to the parent class constructor and this will only be possible if there is a matching constructor there, and @Builder wouldn't generate it.

Also PersonBuilder<> extends PartyBuilder<>, that is why calling super with the child type builder works fine here.

The type parameter for builder() (which represents what kind of Child you are creating) is not inferred correctly. The compiler thinks it's Object. To fix the error, just make it very clear what kind of Child.Builder you are creating, e.g.

Child.<Long>builder()
    ...

The reason for why this cannot be inferred is similar to why chaining thenComparings breaks type inference.

You can see something similar happen with simple builders too:

@Builder
final class Foo<T> {
    private T t;
}

// error here!
Foo<Long> f = Foo.builder().t(1L).build();

Though in simple cases like that, the error message is a lot clearer, saying that you cannot convert a Foo<Object> to Foo<Long>.

Your case is more complicated - you have a SomeGenericClass<?, Parent<T>> field. That means someGenericClass() is expecting a SomeGenericClass<?, Parent<Object>>. A SomeGenericClass<String, Parent<Long>> certainly can't be passed to that. And the fact that you're using SuperBuilder makes things even more complicated.