Well, it works, but somehow only snaps to the left of the first row, not really above the fist row.
As I'm not able to fix this nor "offset" the cursor via addns (I can only use something like SetFocus, and if the focus is set to the left of the row ... I even tried to focus other conrols more to the right, like the item's icon and text. Does not work).
So you'd have to move the mouse straight to the right for a bit after opening the loot window.
Seems the lootwindow is moved after that happens, as the command in chat with the opened loot window
Lua Code:
/script WINDOW_MANAGER:SetMouseFocusByName("ZO_LootAlphaContainerList1Row1")
works just fine.
Guess this was fixed by PP via making the loot window wider/looking different in total.
Edit:
Found a way to select the row now, but the first open will be still more to the left a bit.