If it's already been cleaned and had the thermal paste re-applied, I'm assuming it's a bad thermal paste application, or just crap thermal paste. If it was me, I'd just redo everything, making sure it's all done right. Make sure to clean the APU thoroughly and use enough of a quality thermal paste. Also, be sure the heatsink is mounted to the APU correctly with enough force.
I have an old EVGA GeForce GTX 1060 6GB that ran hot, with the fan running wide open all the time. I originally thought the heatsink/fan combo was inadequate (compact single fan setup). After taking it a apart, applying some Noctua NT-H1, and reassembling it, it ran cooler, boosted higher, and was much quieter. The factory application didn't seem wrong, so my guess was either bad thermal paste or the screws weren't torqued quite enough.
One thing I will say though. Keeping any game console clean will be the biggest help. My PS3 I bought new in 2012, I have NEVER opened and it still runs pretty quietly. My PS4 from 2015, same deal. My two PS4 Pros, well, I haven't played them enough yet to even really gather much in the way of dust inside. Also, having smokey dust build up (from either smoking or fireplaces) and can kill cooling efficiency. That kind of build up needs very thorough cleaning to get that tar buildup off and to prevent more dust from clogging it so easily.
And as a side note, some games just hit the system differently regardless of how demanding they actually are. On my PS4s, I've had some games that to me look equally as demanding and have one run for hours with a nothing more than a slight hum, while the other makes the thing sound a like a jet engine after 8 seconds.
PS4 pro is a single unit. It also can’t be messed with fan curve wise very much.
possibilities I see:
-bad TIM: hope this one isn’t it. Gonna be a pita to fix
-dust on the cooler or fan: this one you can take care of by opening it up and blowing it out with canned air.
-dying fan: still a pita, but less of one than the TIM
all three of em require opening the case which I suspect is not easy. Gonna require a tutorial and probably special bits.
i suggest consulting the Ifixit site for both. LTT May have a code for a discount on a screw driver kit if needed.
