Can not download photo’s from iMac to external drive

My recommendations for you, according to your problem:

1. Check iCloud Settings

• Make sure that your iCloud Photos settings are correctly configured. Go to System Preferences > Apple ID > iCloud and ensure that "Photos" is checked.

2. Check External Drive Format

• Ensure that your LaCie drive is formatted correctly for use with your Mac. It should be formatted as APFS or Mac OS Extended (Journaled) for optimal compatibility.

3. Free Up Space

• Check if there is enough space on your external drive. If it’s nearly full, try deleting some files or moving them elsewhere.

4. Update macOS

• If you haven't already, consider updating to the latest version of macOS. Updates often include bug fixes that can resolve issues like this.

5. Try a Different App

• If the Photos app continues to crash, try using Image Capture (found in Applications) to transfer your photos to the external drive. This app often bypasses issues with the Photos app.

6. Rebuild Photo Library

• If the Photos app is consistently crashing, consider rebuilding your photo library:
  • Hold down the Option and Command keys while opening the Photos app.
  • In the window that appears, choose "Repair" to begin the process. This may take some time.

7. Check for Background Processes

• Sometimes, other background processes can interfere. Make sure there aren’t any large uploads or downloads happening simultaneously that could be slowing down the system.

8. Test with a Different External Drive

• If possible, try connecting a different external drive to see if the issue persists. This can help determine if the problem is with the LaCie drive itself.

9. Check Console for Errors

• Open the Console app (found in Applications > Utilities) to check for any error messages when the Photos app crashes. This may provide clues to the underlying issue.

If none of these steps work, consider reaching out to Apple Support for more assistance.

How is the external drive formatted?

Is that where you have the Photos library located?

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?