I am playing from Android 12. It's impossible to discard items from inventory to the creative menu, or pick items from the inventory to the creative menu.

Steps to reproduce:

Bug 1

1) Play a world in Creative Mode
2) Open the inventory
3) Place any item.
4) Tap on that item.
5) Go to creative menu.
6) Tap anywhere with that item.

Expected: The item must get deleted in the creative menu.

Bug 2
1) Play in Creative Mode
2) Open the inventory.
3) Go to the creative menu.
2) Tap on any item.
3) Go to the inventory.
4) Tap on any slot.

Expected: The item must come in the inventory.