sips

scriptable image processing system. Part of macOS.

convert heic to png or jpg

just one:

sips -s format png image.heic --out image.png
sips -s format jpeg image.heic --out image.jpg

multiple in a loop:

for i in *.heic; do sips -s format png "${i}" --out "${i%.*}.png"; done
for i in *.heic; do sips -s format jpeg "${i}" --out "${i%.heic}.jpg"; done