heif is not supported, any plans for supporting it - see High Efficiency Image File Format - Wikipedia
here is a sample image
sample1.7z (2.4 MB)
Looks pretty supported to me 
Make sure it works in the Windows Photos app first, if you don't already have the Microsoft codec installed.
Saying that, you'll get more support in Opus if you rename the file to .heic instead of .heif.
HEIF = the format
HEIC = the standard extension for the format
It'll only work in the standalone viewer with .heic as the extension.
I'll add .heif to the plugin so it recognises that as well.
it work ony with the Microsoft HEVC Video Extension
alternativ dlls for heic not realy fine supported from windows. i test it always with windows foto.
Microsoft.HEVCVideoExtension_1.0.31823.0_x64.zip from Device Manufacturer is the last free version. if u found it and install it, update the windows store it to the last version 
GL
ps: virustotal is ur friend