GNU/Linux Ubuntu 23.04 Installing Radeon RX 6400 Driver Guide
Hi! The linked Tutorial shows you Step-by-Step How to Install AMD Radeon RX 6400 Graphics and GPU Driver in Ubuntu 23.04 Lunar GNU/Linux 64-bit Desktop.
And there are 2 Radeon RX 6400 Ubuntu Lunar Driver available Alternatives of AMDGPU: Proprietary and Open-Source.
The AMDGPU Pro Software includes Support for Accelerated Graphics, MESA Multimedia, Pro OpenGL, Pro Vulkan and Pro OpenCL.
AMDGPU Driver supports all AMD Radeon GPUs based on the Graphics Core Next (GCN), Radeon DNA (RDNA), and Compute DNA (CDNA) architectures.
Finally, as a good Alternative to the AMDGPU-PRO you should see instead the AMD Open Source Driver Setup.
AMDGPU Ubuntu 23.04 Installation Guide