To convert an HDR PNG that's exported with HLG transfer function in Rec. 2020 color space, do:

avifenc -s 4 -j 4 --min 1 --max 56 -a end-usage=q -a cq-level=18 -a color:deltaq-mode=1 -a tune=ssim \
    -a color:enable-chroma-deltaq=1 -a color:enable-qm=1 -d 12 --cicp 9/18/9 IMG_0186.png IMG_0186.avif

For HDR with PQ transfer function in Rec. 2020 color space, do:

avifenc -s 4 -j 4 --min 1 --max 56 -a end-usage=q -a cq-level=18 -a color:deltaq-mode=1 -a tune=ssim \
    -a color:enable-chroma-deltaq=1 -a color:enable-qm=1 -d 12 --cicp 9/16/9 IMG_0186.png IMG_0186.avif

For the default SDR image (sRGB with BT.601 coefficients), simply do:

avifenc -s 4 -j 4 --min 1 --max 56 -a end-usage=q -a cq-level=18 -a color:deltaq-mode=1 -a tune=ssim \
    -a color:enable-chroma-deltaq=1 -a color:enable-qm=1 --cicp 1/13/6 IMG_0186.png IMG_0186.avif

For the same with BT.709 coefficients, do:

avifenc -s 4 -j 4 --min 1 --max 56 -a end-usage=q -a cq-level=18 -a color:deltaq-mode=1 -a tune=ssim \
    -a color:enable-chroma-deltaq=1 -a color:enable-qm=1 --cicp 1/13/1 IMG_0186.png IMG_0186.avif

Notes:

• -a color:deltaq-mode=1 might be redundant (or ignored)
• If --cicp is ignored and the source image doesn't specify any profile, 2/2/6 is used where 2 means unspecified. This is okay for sRGB.

Sources:

• https://github.com/AOMediaCodec/libavif/wiki/CICP
• https://en.wikipedia.org/wiki/Coding-independent_code_points
• https://old.reddit.com/r/AV1/comments/o7s8hk/high_quality_encoding_of_avif_images_using/
• https://wiki.x266.mov/docs/encoders/aomenc#avif-encoding
• (av1 video) https://www.reddit.com/r/AV1/comments/t59j32/encoder_tuning_part_4_a_2nd_generation_guide_to/
• (av1 video) https://gist.github.com/nico-lab/a6508f283a77696e79a131e07abd86b9