I think “Place - Add lines” should be different as ‘add connected graphic lines’ (currently this is the description).
I expect the connected lines forms background-fillable shape (e.g: arrow head). But the actual thing is just many lines.
While add line just add line, plus line ending option (I see somewhere post this as wishlist).
For a filled shape you need to open the symbol editor and treat the, in your case, arrow head, as a new component in a personal library… a bit messy, but you will have it forever for any future schematic also.
I know there is no function for filling a created polygon such as in the Symbol Editor. That would be a separate “wishlist” item.
The issue I created was just to sort out the descriptions of what is there already.