EDIUS / Mync doesn’t have a codec for  HEIF file as designed. There are below two ways to load the type of clip into EDIUS

1. Convert to JPEG in Windows Photos

1) Download & install HEIF Image Extensions
2) If you would like to import the file from a device, connect it to the PC
3) Run Windows Photos
4) From Import menu, choose either ‘From a folder’ or ‘From a connected device’
5) Import  HEIF file(s). While importing, the application will convert it to JPEG file
6) Converted file will be saved into C:\Users\{USER NAME}\Pictures
7) Load converted file to EDIUS / Mync

2. Use 3rd party converter utility

Use 3rd party converter utility to convert HEIF to JPEG or PNG