So, with configuration like:

 ObjectMapper mapper = JsonMapper.builder()
                .withConfigOverride(Map.Entry.class, cfg ->
                    cfg.setFormat(JsonFormat.Value.forShape(JsonFormat.Shape.OBJECT)))
                .build();

attempts to serialize Map.Entry of JDK Maps (like LinkedHashMap) fails due to access problems (unless --add-opens is used).

There is an existing test that fails this way. But we should be able to have a serializer that works with public API in this case.