Hardware accelerated video decoding / video playback in Chromium seems to be broken (again?).
If I am not entirely mistaken, it used to work in version 101.0.4951.64-1 for both h.264 and vp9 but now, with 102.0.5005.61-1, vp9 videos are played using software decoding (VpxVideoDecoder) only.
As downgrading chromium to 101.0.4951.64-1 did not help, I am assuming that this might be connected to the graphics driver (which is nvidia-dkms 515.43.04-2 on my system), or this libva-vdpau-driver-vp9 package from AUR (is this still needed anyway?).