So I haven't messed with Unity, and hae very poor programming skills. And I don't know how you have things set up.
Internal hotkeys. such as 1-0 for the bar in the overworld wouldn't really need to be displayed. But can be implemented.
But having a lack of knowledge of unity doesn't help. Some program languages have that option. In some way.
Namely it would it would look at the slot, lets say slot one. Default could be "1" So it waits for the touch input, or detects the one key being pressed. But for custom keys. It could read the keybind for slot one, then shows the possible key next to the choice.
But somthing that might not be a horrible option, if other people want it. 1-5 on the left, 6-0 on the right. No custom hotkeys needed. Wont need custom keybinds. Sure playing with a normal keyboard I can't easily play with one hand, But its a better option then when I fat-finger the wrong choice.
Also I don't know if this was mentioned anywhere else. Is exp bugged for me? Whether I fight one monster or four, exp is the same for what I fight. Like Tekr gives 25. If I find one its 25, i find four its still 25.