Hello gunjan290,
Thanks for choosing the Apple Support Communities. We see you want to export photos from your iPhone to an external hard drive. We suggest following the steps below to successfully do this. Give them a try and let us know if you have any questions.
Import and export photos and videos on iPhone - Apple Support
"Export photos and videos to an external storage device
You can export photos and videos you took on your iPhone directly to an external drive, a memory card, or other storage device.
Note: For photos and videos that have been edited, the unmodified original version will be exported.
- Connect your iPhone to the storage device using the Lightning or USB-C connector, or connect the device directly to your iPhone.
- Open the Photos app, then select the photos and videos you want to export.
- Tap
, then tap Export Unmodified Original. - Tap your storage device (below Locations), then tap Save."
We hope this helps.
Cheers!