edit: based on what I could find, I think it's disabling "updated fan controls" under system settings. Must have missed the patch where they added the option.
It’s also worth trying to limit power draw and seeing how far you can go before it impacts performance. This game I’ve been playing went from about 18 watts to 7 watts with very little performance change and the fans run way quieter.
Probably fixed RMA units. I had to RMA my original June 2022 Deck because it got stuck in some permanent low TDP mode. Otherwise the hardware was still in great condition. If they were able to somehow reflash the firmware to fix this issue it would be like new. I'm sure there were others RMA'd for this issue or minor internal hardware issues that could be fixed. If there were fan issues hopefully they put new fans in as part of the refurbishing process.