There is a longer post "FFmpeg qsv_av1" (enabling qsv hw acceleration over 2 pages!) on Intel's support forum. There might be useful troubleshooting details.
https://community.intel.com/t5/Media-Intel-Video-Processing/FFmpeg-qsv-av1/m-p/1539392

Maybe the poster did not finish the last suggestion, but Page 2 near the end, Intel's moderator pointed at an output error:
https://community.intel.com/t5/Media-Intel-Video-Processing/FFmpeg-qsv-av1/td-p/1528124/page/2

Looked at the 2 above urls, but unfortunately they are using avv1 which does not work on any of my computers.

For the above error, this is caused by a recent change in FFmpeg master, unfortunately FFmpeg 6.1 also has this issue.
Could you try FFmpeg 6.0 instead ? Or kindly try this patch:
https://patchwork.ffmpeg.org/project/ffmpeg/patch/20231127060151.2435971-1-haihao.xiang@intel.com/ ?

The above looks like a necessary patch for DECODING, but I was just seeing if I could get ENCODING to work. I will get back to this eventually ! Thanks, Phyllis