For me you need to upgrade your gradle it's better than downgrade JAVA. But for many people it's different. If you think u will upgrade flutter, upgrade gradle is a good solution (upgrade flutter it's good for more compatibility and performance on smartphone). But if you do, you will probably need to update part of your library.

If you don't want to upgrade Flutter, I think you can downgrade JAVA.

I hope my answer will help you or other people