In what cases is the icon with two triangles used (for drop-down lists)?

Question

User interface

Can you formulate an explanation, or maybe you know an article where you can read about the difference between one triangle (the standard drop-down list feature) and two? In what cases is a drop-down list marked with an icon with two triangles?

Answer 1

In this particular case, Yandex was simply mistaken.
Some Yandex designer loves his Mac very much and considers his UI to be the standard.
So I drew it like there, On poppies, this is partly dictated by the fact that the value of the non-editable can be switched with the up and down arrows. This can also be explained by the fact that the list there opens a little trickier (positioned on the selected one) and not always down.
In editable lists there is also 1 triangle.
But in the rest of the world, 2 triangles are made on the Num UP/down element, because Depending on which triangle you click on, the value will increase or decrease. On drop-down lists (any) just a triangle (or tick) to avoid confusion.
just in case, I attach a screenshot from the UI on macs (old, but not of much importance)

Answer 2

Personally, I would expect that this is a separate element from the drop-down menu to increase / decrease the value in the input. (But it's not)
Perhaps a hint that the value can be switched with the arrows on the keyboard.

Answer 3

It seems to me that 1 is used for listing ala cities, rivers, etc., and 2 for typing (Just like on the screen)