Slow photo transfer from iPhone 16 Pro to Mac mini M4

Are you using iCloud to Sync the photos or..... manually Importing the photos into the Mac Mini's Photos App.

see > Transfer photos and videos from your iPhone or iPad to your Mac or PC - Apple Support

If you are using iCloud to Sync Photos, then the photos will not be transferring over the USB-C cable.

If you are manually Importing the photos from iPhone to the Mac mini's Photo App. and it is slow.

1) Try syncing the iPhone in one of the front USB-C port.

2) Try using a different USB-C cable.

Have you tried Airdrop?

if it was me then I would make sure it was connected to the thunderbolt usb-c ports rather than the normal usb usb-c ports