1) Select an item via A hotkey, or long press&hold
2) Close inventory and go to Custom Maps if you selected tiles as your item, or other places for other items (research tree for resources, etc)
3) Sell/Spend all the items selected
4) Go to main menu and open inventory
5) Select any item. It will become long-press selected instantly
6) Deselect that item by pressing on it
7) Now that you have only 1 item selected, you can see it is the item you initially selcted and have already sold/used
8) If the item is a tile, prestige the stack to crash the game