Nouveau is a highly capable open source driver for NVIDIA GPUs based on reverse-engineering.

For some older card generations (e.g. GTX 600 series) it was competitive with the official driver. But in every hardware generation since then, the GPU requires signed firmware in order to run at any decent clock speed.

The necessary signed firmware is present inside the proprietary driver, but nouveau can't load it because it's against the ToS to redistribute it.

Most GPU features are available but run at 0.1x speed or slower because of this single reason. Nvidia could absolutely fix this "tomorrow" if they were motivated.

https://www.phoronix.com/scan.php?page=news_item&px=Nouveau-...