Last month, Sony quietly released a new revision of the PS5 that weighs about 300 grams less than the original model. Why, you ask? Because the new refreshed model has a smaller heatsink, that gives less cooling performance, but there's more to it than just that.
The new PS5 model was tested first by YouTuber Austin Evans in a YouTube video, the temperature test showed that the new PS5 was ~3-5°C hotter than the old model, and concluded that the new heatsink is a sort of a downgrade. The video generated some controversy mainly because he used his phone to measure out the temperatures, and the lack of proper testing.
Now more testing has been done by two more channels, HarwareBusters and GamerNexus. The combined result from both shows that the new PS5 is actually an improvement; the CPU, APU, VRM & memory all run cooler than the old PS5, with 6 to 20°C difference between the two.
Much more detailed explanations are on the YT videos below.