Open the HEIC image in Preview
Click File
Click Export
Choose JPG from the Format menu
Select a save location
Click Save
Select multiple HEIC files in Finder
Right-click and choose Quick Actions
Click Convert Image
Choose JPEG as the format
Click Convert
Open Photos on Mac
Select the HEIC photo
Click File
Click Export
Choose Export Photo
Select JPEG as the file type
Click Export
Use Image Capture to import HEIC photos from an iPhone
Choose a destination folder
Set the file format to JPEG if available
Import the images
Use Automator to create a batch conversion workflow
Add the Change Type of Images action
Set the output format to JPEG
Run the workflow on HEIC files
Use a third-party converter app if needed