Basically, you'd have to change this https://github.com/Globox1997/tiered/blob/1.19/src/main/java/draylar/tiered/reforge/ReforgeScreen.java#L82
to something like
else if (itemStack.getItem() instanceof ArmorItem armorItem) {
if (armorItem.getMaterial().getRepairIngredient() != null) {
baseItems.addAll(Arrays.asList(armorItem.getMaterial().getRepairIngredient().getMatchingStacks()));
}
} else {
...

(Didn't test it for errors and such, but that should avoid the NPE)

latest.log

mh the repair ingredient should not be null but are there other cases like tools which have no ingredient either?

Fixed with 08d3446