First of all,
PlayStation 5 uncovered: the Mark Cerny tech deep dive
"We don't use the actual temperature of the die, as that would cause two types of variance between PS5s," explains Mark Cerny. "One is variance caused by differences in ambient temperature; the console could be in a hotter or cooler location in the room. The other is variance caused by the individual custom chip in the console, some chips run hotter and some chips run cooler. So instead of using the temperature of the die, we use an algorithm in which the frequency depends on CPU and GPU activity information. That keeps behaviour between PS5s consistent."
PS5 has enough power to run the CPU and GPU at max clocks at the same time.
"There's enough power that both CPU and GPU can potentially run at their limits of 3.5GHz and 2.23GHz, it isn't the case that the developer has to choose to run one of them slower."
One thing many people miss is this quote from Cerny.
"The CPU and GPU each have a power budget, of course the GPU power budget is the larger of the two," adds Cerny. "If the CPU doesn't use its power budget - for example, if it is capped at 3.5GHz - then the unused portion of the budget goes to the GPU."
The capped implies even though it's running at max frequency, it isn't using all it's power budget. Which makes any GPU downclocking extremely rare.
Also, Cerny somewhat explained a situation when the GPU consumes more power than usual, which causes the GPU to downclock to keep heat in check.
"It's about the minutiae of what's being displayed and how."
"It's counterintuitive but processing dense geometry typically consumes less power than processing simple geometry, which is why I suspect Horizon's map screen with its low triangle count makes my PS4 Pro heat up so much."
I know it can drop 1 frame in the 60fps mode, but I don't know if that's what you're experiencing.
Are you sure you're not running it on unlocked 60fps?
Maybe some links showing us the frame rate drop on the PS5 version would be nice to help us solve this mystery.