Engine overheating reduce speed

My 2011 XC60 displayed this warning today and I’m trying to figure out why. Was it because I was driving around a hilly area looking for parking? I smelled burning and turned the car off. It’s sitting parked and cooling down currently. I don’t want to mess with it or open the hood until it’s cooled down.

The car overheated a few months ago due to the owner before me putting in the wrong size serpentine belt which caused a whole host of issues. I can name that the AC seems to have been having some issues recently. It goes in and out. If I’m parked it doesn’t blow cold air. I’m not sure if this is related or not!

What is usually the issue when this warning is displayed?

Thanks