Browser video and monitoring
Hardware video decode needs a kernel with VCN support, see Hardware video (VCN). With it, browsers can decode H.264 video on the GPU instead of the CPU.
Chrome
Put these flags in ~/.config/chrome-flags.conf:
--ozone-platform=wayland
--enable-features=AcceleratedVideoDecodeLinuxGL,AcceleratedVideoDecodeLinuxZeroCopyGL,AcceleratedVideoEncoder,VaapiIgnoreDriverChecks
Restart Chrome. Open chrome://gpu and check that Video Decode reads as hardware accelerated. The file is read by Arch-based packages of Chrome. Other packages may need the flags on the command line.
Firefox
Firefox uses hardware decode by default when VAAPI works. No flags are needed.
YouTube and AV1
The GPU has no AV1 decoder, so AV1 video falls back to the CPU and can stutter. Use an extension such as enhanced-h264ify to make YouTube serve H.264.
Read GPU load
On the original PS5 and the Slim the GPU has no load sensor in the kernel, so KDE's system monitor shows no GPU usage; nvtop in a terminal shows what the driver does know. On the PS5 Pro the SMU backend provides gpu_busy_percent, and overlays such as MangoHud show the load.
The Chrome flags were reported on the official CachyOS image. The encoder flag turns on hardware encode, which only works well with H.264, see Using it with FFmpeg.