Update: I fixed this by opening the back panel and unplug, then reconnect the fan cable (the white 4 pin connector). It felt a bit loose for me, so you maybe just need to just need to reassure connector sits properly in place.
The fan went crazy and the system have now been on cooldown for around 30 min. The fan is still going at full speed when the system gets power. We played Sims 4 a couple of hours, no active downloads in the background.
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