The High Efficiency Image File (HEIF) format is the default when airdropping an image from an iPhone to a OSX device. I want to edit and modify these .HEIC files with Python.>
I am facing the exact same problem as you, wanting a CLI solution. Doing some further research, it seems ImageMagick requires the libheif delegate library. The libheif library itself seems to have some dependencies as well.
I have not had success in getting any of those to work as well, but will continue trying. I suggest you check if those dependencies are available to your configuration.