Ryzen 8600G undervolted and with negative frequency offset. 10 minutes of Cinebench - CPU reaches only 61C with no CPU cooler fans and no case fans.
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At low loads (when browsing internet etc.) the CPU temperature doesn't go far beyond 35C, that's in 22C room. The CPU cooler is Thermalright Frost Spirit 140 - 1kg of radiator. This cooler is discontinued, there's one called Peerless Assassin 140 that has a similar in size radiator. So no elaborate cooling solution is needed, just a radiator that sells for 40$ on Amazon.
Temperatures these low are achieved because the CPU is actually a mobile APU, it is designed to operate at low voltages. Also, it has a big silicon surface which helps with heat dissipation. Undervolting makes it even cooler.
The GPU is not needed as the CPU has built-in graphics, which is btw very modern and has all the latest features, live av1 decoder and even encoder. PSU is silent when the load is light, which is always the case as the CPU cannot draw a lot of power. And the rest of the computer is just storage. I've been running it for months like this with no fans inside the case - no issues.