It is a known problem. Every generation of Pi has been a little bit hotter than the previous. Pi4 runs very hot - not just the CPU but several other components on the board are generating more heat than previous generation. The result is that many people consider active cooling necessary.
Flirc case will help to cool the CPU a little bit but it is a bad design because it's a mostly-sealed metal box and only sinks heat from the CPU. With many other components generating more heat, the air inside will heat up something terrible and it will slowly cook your RPi. The material also makes it much harder to cut holes for venting or add a fan.
I wonder how the Pi 4 will behave with enclosures such as these that are basically one large heat sink for all chips.Would make it easy to carry around also. I refuse to rely on active cooling. A Pi has to be completely silent to begin with, and I travel quite a lot so the less parts and wires that can break the better.