I'm seeing the same problem. Debug information below.

LIBVA_MESSAGING_LEVEL=2 snap run chromium
[20382:20382:0821/200854.560443:ERROR:sandbox_linux.cc(374)] InitializeSandbox() called with multiple threads in process gpu-process.
[20548:13:0821/200904.074169:ERROR:batching_media_log.cc(38)] MediaEvent: {"error":"{\"causes\":[{\"causes\":[],\"data\":{},\"stack\":[{\"file\":\"../../media/filters/decrypting_video_decoder.cc\",\"line\":53}],\"status_code\":264,\"status_message\":\"\"}],\"data\":{\"Decoder name\":\"DecryptingVideoDecoder\"},\"stack\":[{\"file\":\"../../media/filters/decoder_selector.cc\",\"line\":172}],\"status_code\":265,\"status_message\":\"\"}"}
[20248:20383:0821/200904.173566:ERROR:object_proxy.cc(622)] Failed to call method: org.freedesktop.PowerManagement.Inhibit.Inhibit: object_path= /org/freedesktop/PowerManagement/Inhibit: org.freedesktop.DBus.Error.AccessDenied: An AppArmor policy prevents this sender from sending this message to this recipient; type="method_call", sender=":1.504" (uid=1000 pid=20248 comm="/snap/chromium/1260/usr/lib/chromium-browser/chrom" label="snap.chromium.chromium (enforce)") interface="org.freedesktop.PowerManagement.Inhibit" member="Inhibit" error name="(unset)" requested_reply="0" destination="org.freedesktop.PowerManagement" (uid=1000 pid=1571 comm="xfce4-power-manager " label="unconfined")
[20248:20383:0821/200904.173588:ERROR:power_save_blocker_linux.cc(373)] No response to Inhibit() request!
[20248:20383:0821/200904.379145:ERROR:object_proxy.cc(622)] Failed to call method: org.freedesktop.PowerManagement.Inhibit.Inhibit: object_path= /org/freedesktop/PowerManagement/Inhibit: org.freedesktop.DBus.Error.AccessDenied: An AppArmor policy prevents this sender from sending this message to this recipient; type="method_call", sender=":1.505" (uid=1000 pid=20248 comm="/snap/chromium/1260/usr/lib/chromium-browser/chrom" label="snap.chromium.chromium (enforce)") interface="org.freedesktop.PowerManagement.Inhibit" member="Inhibit" error name="(unset)" requested_reply="0" destination="org.freedesktop.PowerManagement" (uid=1000 pid=1571 comm="xfce4-power-manager " label="unconfined")
[20248:20383:0821/200904.379183:ERROR:power_save_blocker_linux.cc(373)] No response to Inhibit() request!
[20248:20248:0821/200913.822437:ERROR:event_router.cc(713)] Event dispatched while shutting down extensions browser client.

libva info: VA-API version 1.8.0
libva info: Trying to open /usr/lib/x86_64-linux-gnu/dri/iHD_drv_video.so
libva info: Found init function __vaDriverInit_1_8
libva info: va_openDriver() returns 0
vainfo: VA-API version: 1.8 (libva 2.1.0)
vainfo: Driver version: Intel iHD driver for Intel(R) Gen Graphics - 20.2.pre (f403839f)
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
      VAProfileVP8Version0_3          :	VAEntrypointEncSlice
      VAProfileHEVCMain               :	VAEntrypointVLD
      VAProfileHEVCMain               :	VAEntrypointEncSlice
      VAProfileHEVCMain               :	VAEntrypointFEI
      VAProfileHEVCMain10             :	VAEntrypointVLD
      VAProfileHEVCMain10             :	VAEntrypointEncSlice
      VAProfileVP9Profile0            :	VAEntrypointVLD
      VAProfileVP9Profile2            :	VAEntrypointVLD

audio_buffering_state	{"state":"BUFFERING_HAVE_ENOUGH"}
dimensions	"1920x988"
duration	243.981
error	"{\"causes\":[{\"causes\":[],\"data\":{},\"stack\":[{\"file\":\"../../media/filters/decrypting_video_decoder.cc\",\"line\":53}],\"status_code\":264,\"status_message\":\"\"}],\"data\":{\"Decoder name\":\"DecryptingVideoDecoder\"},\"stack\":[{\"file\":\"../../media/filters/decoder_selector.cc\",\"line\":172}],\"status_code\":265,\"status_message\":\"\"}"
event	"kPlay"
info	"Selected video track: []"
kAudioDecoderName	"FFmpegAudioDecoder"
kAudioTracks	[{"bytes per channel":4,"bytes per frame":8,"channel layout":"STEREO","channels":2,"codec":"opus","codec delay":312,"discard decoder delay":true,"encryption scheme":"Unencrypted","has extra data":true,"profile":"unknown","sample format":"Float 32-bit","samples per second":48000,"seek preroll":"80000us"}]
kFrameTitle	""
kFrameUrl	"https://www.youtube.com/watch?v=_l6sbhjm8pk"
kIsAudioDecryptingDemuxerStream	false
kIsPlatformAudioDecoder	false
kIsPlatformVideoDecoder	false
kIsVideoDecryptingDemuxerStream	false
kResolution	"1920x988"
kVideoDecoderName	"VpxVideoDecoder"
kVideoTracks	[{"alpha mode":"is_opaque","codec":"vp9","coded size":"1920x988","color space":"{primaries:BT709, transfer:BT709, matrix:BT709, range:LIMITED}","encryption scheme":"Unencrypted","has extra data":false,"hdr metadata":"unset","natural size":"1920x988","orientation":"0°","profile":"vp9 profile0","visible rect":"0,0 1920x988"}]
origin_url	"https://www.youtube.com/"
pipeline_buffering_state	{"for_suspended_start":false,"state":"BUFFERING_HAVE_ENOUGH"}
pipeline_state	"kPlaying"
player_id	43
render_id	27
url	"blob:https://www.youtube.com/a1cf0fdf-8d73-4a23-ba8d-f984c18dfaa6"
video_buffering_state	{"state":"BUFFERING_HAVE_ENOUGH"}