If the ascents are a little longer than a short hike to the start of the next powder run, it is advisable to take off your goggles and helmet and stow them in your backpack. The lens does not fog up, but the foam absorbs sweat from the forehead, just like any other ski goggles. If your head does overheat on the ascent despite being as fit as Dario Cologna, the helmet is probably the cause and not the goggles. But in some situations I was very grateful for the significant increase in ventilation. For example, when I missed the traverse back to the lift on my local mountain and only realized a few metres later that it was too late to cross. So I had to unbuckle my skis and trudge up. I left my helmet and goggles on. I thought to myself, it's really cold and it won't be that hard to trudge back the few meters. It's all a question of stamina! After a short time, I was extremely grateful to be able to open the goggles - even with my thick winter gloves on, it went well. However, I will probably have to work on my fitness a bit more. The fact that I missed the traverse was certainly not due to a lack of visibility, but rather a lack of understanding that every powder run has to come to an end at some point!
I don't know whether the developers of the goggles saw corona coming when they were created, but putting the lens up helps enormously against fogging when wearing a protective mask, e.g. when queuing for the lift.
