I have a question Is it possible to clear 1-1 100% with Nabbit? Why didn't anyone try to Acorn plains 1

The game doesn't register any level cleared by Nabbit as 100%.

When you normally complete a level with Nabbit, the color of the level on the world map is purple rather than blue, meaning that the game doesn't register the level as being fully "beaten." Also, its impossible to get a 5 star save file if any of the levels are still purple, so we decided to ban all Nabbit 100% ILs from the boards.