See this image:
Do you have physical access to the unit?, can you gain access and check the screen’s model?.
J is MY18 I believe, or at least it originally was. Maybe J-series is a “transition” serie between MY20 and NOT-MY20?, not sure…
Check this other thread: → Black screen after update
If in fact your screen is MY20, if you can get hand to a not MY20 screen you could complete the update.