It is completely wrong. It makes them easier to get spotted 1000% easier and gives them no benefit.
It is simply a death sentence to any medieval warrior.
The Mongols preferred brown armours as leathers were turned brown due to the sun and smoke drying process. The thick leathers were never white, and this armour is just so wrong. Any light cavalry was expected to have at least leather armour and to have nature-friendly colour brown, darker brown, red-brown, etc.
These kinds of armours were effective for camouflaging and making them harder to get noticed in the woods or in bushy terrains etc. On the steppe, everything gets noticed so colour didn’t matter.
With this white armour, anyone can see a Mongol army from miles away in any type of terrain
Therefore, I suggest changing the armour to a more brownish colour as it would make it more cooler and accurate.
The AOE4 mangudai’s hat is more of a modern one that is worn by wrestlers (the most common one)
It is worn on special occasions and is not really combat-focused, especially not for mounted warfare
So please change the hat of the Mangudai model.
It can be like the picture I have shared or any other hat that the game has for the Mongols.