As everyone else has said: The Noveau driver has really bad performance, bad compatibility, bad stability, and almost no ability to support the special hardware of the Tegra systems.
The 3D support you get with the built-in Tegra driver and OpenGL 4.3 on the Jetson Nano is miles better than the Noveau variant. OpenGL is an open API.
The video encoding and decoding support you get with the built-in Tegra driver (using the V4L2 codec API, examples are in the examples folder) is miles better than Noveau, and it’s very unlikely that Noveau would even support the Tegra video accelerators, as those look different than the desktop variants. V4L2 is an open API.
You’re already 100% dependent on NVIDIA because they made the hardware you’re running on. Trying to remove a small vendor dependency by using Noveau instead of Tegra drivers is a little bit like trying to save on gas mileage by turning off your car headlights at night. Not only doesn’t it do much, it’s actually a really bad idea.
I recommend using the Linux4Tegra installation provided by NVIDIA, and the Tegra drivers that come with it, and enjoy the system as it is! Develop applications on top of the open OpenGL and Video4Linux APIs, and if you somehow decide you don’t want to depend on NVIDIA anymore, you can port it to other hardware because those are open APIs.