Ikmos allows creation of every unobtainable item in super flat survival.
When you create your world you can choose to have access to the new item 'Item Core" by game rules by doing so you start with an item core without having to craft it. That items allows you to create the other unobtainable items in minecraft superflat.
AS A REMINDER CERATE YOUR WORLD IN 1.17.1 BEFORE UPGRADING TO 1.18.2