When you are in the menu, click on Inventory and then you will see four tabs [Inverntory | Weapon | Clothes | Key Items] - you have to click on Invetory tab and only then you will be able to click on flowers to consume them. It is not very intuitive.
It’s not, but it’s a part of basic menu system - we can change only if completely remastering the menu system which we can’t do right now (however can in the future)