CUDA 11 is incompatible with the Nano. Jetsons have an integrated GPU (iGPU), whereas most computers (desktop PCs) have a discrete GPU (dGPU). The iGPU is directly wired to the memory controller instead of going through the PCI bus. This means the drivers are not the same as the general PCI drivers, and that the iGPU driver is tied to the specific L4T release on the Jetson (L4T is Ubuntu plus NVIDIA drivers…this is what gets installed when flashing, whereas JetPack/SDK Manager is the software on the PC which performs the flash of L4T; a specific L4T release is tied to a specific JetPack release). The releases of L4T which are compatible with CUDA 11 are all from releases which do not exist for the Nano. Whatever driver you installed is not for an iGPU and will basically break the GPU driver.