When I turn on inventory++ and put something inside of the crafting area, when I close my inventory it goes back into the actual inventory.
I use 1.16.5, vanilla launcher. Mods are WorldEdit and RoughlyEnoughItems. I tested it without those mods and it didn't work. I also tested it without the mods in the built in addons, and it still didn't work.
If i close my inventory in this picture, the dirt would go into the fifth hotbar slot.