Look up "nouveau signed firmware". Phoronix has a bunch of articles on it. The Nouveau developers also talk about it at FOSDEM 2018 (and probably a later conference). This comment is a good intro: https://www.phoronix.com/forums/forum/linux-graphics-x-org-d...

TL;DR starting with the 9xx series, Nvidia started making it so their GPUs would only run firmwares signed by them (likely to prevent counterfeits, i.e. 2060s sold as 2080s). So it is impossible to control the fans and reclock the GPU. There's no workaround, so even as the person who owns the device, I can't run my own firmware. AMD has signed firmwares too, but they actually release sufficient blobs to fully run the device.