So you wanna use some photos you “shot on iPhone” but your app doesn't support .HEIC?
jpg
fast, lossy, smaller files
find . -maxdepth 1 -type f -iname '*.heic' -print0 | xargs -0 -I{} sh -c 'sips -s format jpeg "$1" --out "${1%.*}.jpg"' sh "{}"
png
slow, lossless, larger files
find . -maxdepth 1 -type f -iname '*.heic' -print0 | xargs -0 -I{} sh -c 'sips -s format png "$1" --out "${1%.*}.png"' sh "{}"