Your iPhone photos are in HEIC format, but you need JPG. Here are three ways to convert them on your Mac — completely free.
For batch conversion, select multiple HEIC files in Finder, right-click → Open With → Preview, then select all in the sidebar and Export.
heic-tool.com works on Mac browsers (Safari, Chrome, Firefox). Drag your files in, click convert, download the JPG. No upload needed — everything happens locally on your Mac.
Create a right-click quick action on Mac: open Automator → New Quick Action → add "Change Type of Images" → set to JPEG → save. Now you can right-click any HEIC file in Finder and select your quick action to batch convert.