How can I view .HEIC photos on Linux?

For local conversion, this worked for me in Debian. Just downloaded the static build, ran the example conversion command, everything worked:

https://github.com/monostream/tifig

.heic may be the file name extension, but the format is more commonly known as HEIF, the High Efficiency Image File format. There’s an open source implementation from Nokia here: http://nokiatech.github.io/heif/

You could convert it to a supported format using ffmpeg:

ffmpeg -i image.heic image.png