TypeError: can only concatenate list (not “str”) to list

I think what you want to do is add a new item to your list, so you have change the line newinv=inventory+str(add) with this one:

newinv = inventory.append(add)

What you are doing now is trying to concatenate a list with a string which is an invalid operation in Python.

However I think what you want is to add and delete items from a list, in that case your if/else block should be:

if selection=="use":
    print(inventory)
    remove=input("What do you want to use? ")
    inventory.remove(remove)
    print(inventory)

elif selection=="pickup":
    print(inventory)
    add=input("What do you want to pickup? ")
    inventory.append(add)
    print(inventory)

You don’t need to build a new inventory list every time you add a new item.