System: EndeavourOS, kernel 6.18.22-1-lts, Wayland, NVIDIA GeForce RTX 5060 Ti (GB206)
Packages: libva-nvidia-driver 0.0.16-1 (also tested git version), nvidia-open-dkms 595.58.03-1
Browsers tested: brave-bin (AUR) and chromium (official repo)
vainfo shows full HEVC support (Main, Main10, Main444) with VA-API 1.23 / NVDEC driver
brave://gpu lists HEVC in Video Decode as hardware accelerated
H.264 hardware decoding works fine — only HEVC is broken
No iGPU present (only the RTX 5060 Ti)
Firefox HEVC hardware decoding works without issues on the same system.
Error in all cases: "VaapiVideoDecoder: failed Initialize()ing the frame pool" at vaapi_video_decoder.cc:1219

=== Wayland tests ===

1. Original flags + --enable-global-vaapi-lock (suggested in Arch forums post #1178)
   NVD_BACKEND=direct
   --enable-features=AcceleratedVideoEncoder,VaapiVideoEncoder,PlatformHEVCEncoderSupport,WebRtcAllowH265Send,WebRtcAllowH265Receive
   --enable-global-vaapi-lock
   Result: frame pool error

2. Added VaapiVideoDecoder, VaapiIgnoreDriverChecks, PlatformHEVCDecoderSupport
   NVD_BACKEND=direct
   --enable-features=AcceleratedVideoEncoder,VaapiVideoEncoder,VaapiVideoDecoder,VaapiIgnoreDriverChecks,PlatformHEVCDecoderSupport,PlatformHEVCEncoderSupport,WebRtcAllowH265Send,WebRtcAllowH265Receive
   --enable-global-vaapi-lock
   Result: frame pool error

3. Switched to NVD_BACKEND=egl (same flags as #2)
   Result: frame pool error

4. Added --disable-features=UseChromeOSDirectVideoDecoder
   NVD_BACKEND=direct
   Result: frame pool error

5. --use-gl=egl
   Result: completely disables ALL hardware acceleration (everything falls back to software)

6. AcceleratedVideoDecodeLinuxGL path (from nvidia-vaapi-driver#420)
   NVD_BACKEND=direct
   --enable-features=AcceleratedVideoDecodeLinuxGL,AcceleratedVideoDecodeLinuxZeroCopyGL,VaapiOnNvidiaGPUs,VaapiIgnoreDriverChecks,PlatformHEVCDecoderSupport,PlatformHEVCEncoderSupport,WebRtcAllowH265Send,WebRtcAllowH265Receive
   Result: frame pool error

7. Same as #6 with NVD_BACKEND=egl
   Result: frame pool error

8. Same as #6 with --enable-global-vaapi-lock + NVD_BACKEND=direct
   Result: frame pool error

9. Same as #6 with --enable-global-vaapi-lock + NVD_BACKEND=egl
   Result: frame pool error

10. Minimal flags from solved Arch forums thread (https://bbs.archlinux.org/viewtopic.php?id=307713)
    NVD_BACKEND=direct
    --ozone-platform=wayland --enable-features=AcceleratedVideoDecodeLinuxGL,AcceleratedVideoDecodeLinuxZeroCopyGL,VaapiOnNvidiaGPUs,VaapiIgnoreDriverChecks
    Result: frame pool error

11. Plain chromium (official repo) with no flags
    Result: frame pool error

12. libva-nvidia-driver-git (latest master) instead of 0.0.16
    Result: frame pool error

=== X11/XWayland tests ===

13. X11 with minimal flags
    NVD_BACKEND=direct
    --ozone-platform=x11 --enable-features=AcceleratedVideoDecodeLinuxGL,AcceleratedVideoDecodeLinuxZeroCopyGL,VaapiOnNvidiaGPUs,VaapiIgnoreDriverChecks
    Result: frame pool error

14. X11 with VaapiVideoDecoder
    NVD_BACKEND=direct
    --ozone-platform=x11 --enable-features=VaapiVideoDecoder,VaapiIgnoreDriverChecks,VaapiOnNvidiaGPUs,PlatformHEVCDecoderSupport
    Result: frame pool error

15. X11 with egl backend
    NVD_BACKEND=egl
    --ozone-platform=x11 --enable-features=AcceleratedVideoDecodeLinuxGL,AcceleratedVideoDecodeLinuxZeroCopyGL,VaapiOnNvidiaGPUs,VaapiIgnoreDriverChecks
    Result: frame pool error

16. X11 with --use-gl=egl
    NVD_BACKEND=direct
    --ozone-platform=x11 --use-gl=egl --enable-features=AcceleratedVideoDecodeLinuxGL,AcceleratedVideoDecodeLinuxZeroCopyGL,VaapiOnNvidiaGPUs,VaapiIgnoreDriverChecks
    Result: frame pool error

=== Conclusion ===

HEVC decoding via VA-API in Chromium is broken on the RTX 5060 Ti (GB206/Blackwell)
with all 16 tested combinations of libva-nvidia-driver versions, backends, display
protocols (Wayland/X11), and Chromium flags.
H.264 works fine through the same VA-API path, so the issue is HEVC-specific.
Firefox HEVC hardware decoding works without issues on the same system.
This may be related to the RTX 50 series (Blackwell) being very new hardware.