but can you check two more things with cmd line ffmpeg?

first change .webm part of working command line to .mp4

try it and report if and how it fail

and then to mkv

also report if it work or not.

so we will try more common (for now ) container formats for av1, may be 7.0 simply can't make AV1 IN mp4 container ....?

mp4 and mkv works like webm from ffmpeg command line:

du -sh dv01_07_av1_qsv_pr4_bv1570k.*
24M    dv01_07_av1_qsv_pr4_bv1570k.mkv
24M    dv01_07_av1_qsv_pr4_bv1570k.mp4
24M    dv01_07_av1_qsv_pr4_bv1570k.webm

Verified video and audio used with ffprobe :

ffprobe -hide_banner dv01_07_av1_qsv_pr4_bv1570k.mkv
Input #0, matroska,webm, from 'dv01_07_av1_qsv_pr4_bv1570k.mkv':
  Metadata:
    TIMECODE        : 01:09:35:09
    ENCODER         : Lavf61.1.100
  Duration: 00:01:53.29, start: -0.007000, bitrate: 1724 kb/s
  Stream #0:0: Video: av1 (libdav1d) (Main), yuv420p(tv, bottom coded first (swapped)), 720x576, SAR 16:15 DAR 4:3, 25 fps, 25 tbr, 1k tbn
      Metadata:
        ENCODER         : Lavc61.3.100 av1_qsv
        DURATION        : 00:01:53.280000000
  Stream #0:1: Audio: opus, 48000 Hz, stereo, fltp
      Metadata:
        ENCODER         : Lavc61.3.100 libopus
        DURATION        : 00:01:53.288000000
---------

ffprobe -hide_banner dv01_07_av1_qsv_pr4_bv1570k.mp4
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'dv01_07_av1_qsv_pr4_bv1570k.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomav01iso2mp41
    encoder         : Lavf61.1.100
  Duration: 00:01:53.28, start: 0.000000, bitrate: 1768 kb/s
  Stream #0:0[0x1](und): Video: av1 (libdav1d) (Main) (av01 / 0x31307661), yuv420p(tv, bottom coded first (swapped)), 720x576, 1634 kb/s, SAR 16:15 DAR 4:3, 25 fps, 25 tbr, 12800 tbn (default)
      Metadata:
        handler_name    : VideoHandler
        vendor_id       : [0][0][0][0]
        encoder         : Lavc61.3.100 av1_qsv
        timecode        : 01:09:35:09
  Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
      Metadata:
        handler_name    : SoundHandler
        vendor_id       : [0][0][0][0]
  Stream #0:2[0x3](eng): Data: none (tmcd / 0x64636D74)
      Metadata:
        handler_name    : TimeCodeHandler
        timecode        : 01:09:35:09
Unsupported codec with id 0 for input stream 2
---------

ffprobe -hide_banner dv01_07_av1_qsv_pr4_bv1570k.webm
Input #0, matroska,webm, from 'dv01_07_av1_qsv_pr4_bv1570k.webm':
  Metadata:
    TIMECODE        : 01:09:35:09
    ENCODER         : Lavf61.1.100
  Duration: 00:01:53.29, start: -0.007000, bitrate: 1724 kb/s
  Stream #0:0: Video: av1 (libdav1d) (Main), yuv420p(tv), 720x576, SAR 16:15 DAR 4:3, 25 fps, 25 tbr, 1k tbn
      Metadata:
        ENCODER         : Lavc61.3.100 av1_qsv
        DURATION        : 00:01:53.280000000
  Stream #0:1: Audio: opus, 48000 Hz, stereo, fltp
      Metadata:
        ENCODER         : Lavc61.3.100 libopus
        DURATION        : 00:01:53.288000000

sorry for such long road ...