I have exactly same question and according to the sales advertisement this panel light can be installed on the surface, so you do not need a hole in the roof for the panel or for the transformer.
I bought this from aliexpress and got it today, but there is nothing with it I could install it on the roof surface. Also the 1.3cm is kind of face info as the transformer is much taller.
So some special connection rods etc is needed especially made for this panel light is needed in order to be able to install it on the surface like on the sales advertisements seen on internet.
Lets see how my seller answers to my dispute at Aliexpress.
I suppose I will get these missing installation rods etc from this seller in order to install it like on the pictures ( On the roof surface - not built in! )
So, sad that there is totally wrong information on marketing material or no one knows from the retailers how to order these accessories for ceiling surface installation.
So the plan was to have nice lamp at laundry room ceiling, but now this goes to garage…