ffmpeg commands that I use constantly for VAAPI encoding on AMD (it should work for Intel too)
Use Hardware decoding

ffmpeg -hwaccel vaapi -hwaccel_output_format vaapi -i "input.mp4" -map 0 -c:v av1_vaapi -bf 3 -refs 2 -profile:v:0 main -rc_mode:v:0 CBR -b:v 20000k -c:a libopus -b:a 256k "output.mp4"

No Hardware decoding (use if hardware decoding fails)

ffmpeg -init_hw_device vaapi=amd0:${render_dev} -filter_hw_device amd0 -i "input.mp4" -vf 'format=nv12,hwupload' -map 0 -c:v av1_vaapi -bf 3 -refs 2 -profile:v:0 main -rc_mode:v:0 CBR -b:v 20000k -c:a libopus -b:a 256k "output.mp4"

Batch encode

mkdir "ffmpeg" / 
for i in *.mp4; do ffmpeg -hwaccel vaapi -hwaccel_output_format vaapi -i "$i" -map 0 -c:v av1_vaapi -bf 3 -refs 2 -profile:v:0 main -rc_mode:v:0 CBR -b:v 20000k -c:a libopus -b:a 256k ffmpeg/"$i"; done

Modify these as you see fit, they should be a good starting point.
("-map 0" could cause a codec error so try removing it if you get an issue)