правильный ответ - требовался пакет intel-media-driver. В Вики этот пакет упоминался лишь как "вынос некоторых задач...". Но не некоторых, а по существу всех, связанных с проигрыванием видео. ВОт теперь да, -

vainfo
Trying display: wayland
Trying display: x11
vainfo: VA-API version: 1.20 (libva 2.20.0)
vainfo: Driver version: Intel iHD driver for Intel(R) Gen Graphics - 23.3.5 ()
vainfo: Supported profile and entrypoints
      VAProfileNone                   :	VAEntrypointVideoProc
      VAProfileNone                   :	VAEntrypointStats
      VAProfileMPEG2Simple            :	VAEntrypointVLD
      VAProfileMPEG2Simple            :	VAEntrypointEncSlice
      VAProfileMPEG2Main              :	VAEntrypointVLD
      VAProfileMPEG2Main              :	VAEntrypointEncSlice
      VAProfileH264Main               :	VAEntrypointVLD
      VAProfileH264Main               :	VAEntrypointEncSlice
      VAProfileH264Main               :	VAEntrypointFEI
      VAProfileH264Main               :	VAEntrypointEncSliceLP
      VAProfileH264High               :	VAEntrypointVLD
      VAProfileH264High               :	VAEntrypointEncSlice
      VAProfileH264High               :	VAEntrypointFEI
      VAProfileH264High               :	VAEntrypointEncSliceLP
      VAProfileVC1Simple              :	VAEntrypointVLD
      VAProfileVC1Main                :	VAEntrypointVLD
      VAProfileVC1Advanced            :	VAEntrypointVLD
      VAProfileJPEGBaseline           :	VAEntrypointVLD
      VAProfileJPEGBaseline           :	VAEntrypointEncPicture
      VAProfileH264ConstrainedBaseline:	VAEntrypointVLD
      VAProfileH264ConstrainedBaseline:	VAEntrypointEncSlice
      VAProfileH264ConstrainedBaseline:	VAEntrypointFEI
      VAProfileH264ConstrainedBaseline:	VAEntrypointEncSliceLP
      VAProfileVP8Version0_3          :	VAEntrypointVLD
      VAProfileHEVCMain               :	VAEntrypointVLD
      VAProfileHEVCMain               :	VAEntrypointEncSlice
      VAProfileHEVCMain               :	VAEntrypointFEI
      VAProfileHEVCMain               :	VAEntrypointEncSliceLP
      VAProfileHEVCMain10             :	VAEntrypointVLD
      VAProfileHEVCMain10             :	VAEntrypointEncSlice
      VAProfileHEVCMain10             :	VAEntrypointEncSliceLP
      VAProfileVP9Profile0            :	VAEntrypointVLD
      VAProfileVP9Profile0            :	VAEntrypointEncSliceLP
      VAProfileVP9Profile1            :	VAEntrypointVLD
      VAProfileVP9Profile1            :	VAEntrypointEncSliceLP
      VAProfileVP9Profile2            :	VAEntrypointVLD
      VAProfileVP9Profile2            :	VAEntrypointEncSliceLP
      VAProfileVP9Profile3            :	VAEntrypointVLD
      VAProfileVP9Profile3            :	VAEntrypointEncSliceLP
      VAProfileHEVCMain12             :	VAEntrypointVLD
      VAProfileHEVCMain12             :	VAEntrypointEncSlice
      VAProfileHEVCMain422_10         :	VAEntrypointVLD
      VAProfileHEVCMain422_10         :	VAEntrypointEncSlice
      VAProfileHEVCMain422_12         :	VAEntrypointVLD
      VAProfileHEVCMain422_12         :	VAEntrypointEncSlice
      VAProfileHEVCMain444            :	VAEntrypointVLD
      VAProfileHEVCMain444            :	VAEntrypointEncSliceLP
      VAProfileHEVCMain444_10         :	VAEntrypointVLD
      VAProfileHEVCMain444_10         :	VAEntrypointEncSliceLP
      VAProfileHEVCMain444_12         :	VAEntrypointVLD
      VAProfileHEVCSccMain            :	VAEntrypointVLD
      VAProfileHEVCSccMain            :	VAEntrypointEncSliceLP
      VAProfileHEVCSccMain10          :	VAEntrypointVLD
      VAProfileHEVCSccMain10          :	VAEntrypointEncSliceLP
      VAProfileHEVCSccMain444         :	VAEntrypointVLD
      VAProfileHEVCSccMain444         :	VAEntrypointEncSliceLP
      VAProfileAV1Profile0            :	VAEntrypointVLD
      VAProfileHEVCSccMain444_10      :	VAEntrypointVLD
      VAProfileHEVCSccMain444_10      :	VAEntrypointEncSliceLP

итого стоят пакеты -

pacman -Qs intel
local/intel-gmmlib 22.3.12-1
    Intel Graphics Memory Management Library
local/intel-media-driver 23.3.5-1
    Intel Media Driver for VAAPI — Broadwell+ iGPUs
local/intel-ucode 20230808-1
    Microcode update files for Intel CPUs
local/libmfx 23.2.2-2
    Intel Media SDK dispatcher library
local/libva-utils 2.20.0-1
    Intel VA-API Media Applications and Scripts for libva