Open the HEIC file in Preview
Click File
Click Export
Choose JPG as the format
Select a save location
Click Save
Select multiple HEIC files in Finder
Right-click and choose Open With > Preview
In Preview, go to File
Click Export Selected Images
Choose JPG as the format
Click Choose
Open Photos on Mac
Import the HEIC images
Select the images
Click File
Click Export
Choose JPEG as the photo kind
Set the quality if needed
Click Export
Use Automator to create a Quick Action for image conversion
Use the Shortcuts app to build a workflow that converts HEIC to JPG
Use Terminal with the sips command to convert HEIC files to JPG
Change iPhone camera settings to capture in Most Compatible format to avoid HEIC files in the future