Here are a few methods you might find helpful to resolve the issue with Photos freezing during export:
1)Restart Your Computer: Sometimes, simply restarting your computer can resolve temporary software glitches. Give it a try and see if it helps.
2)Check for Software Updates: Make sure both your operating system and Photos app are updated to the latest version. Updates often include bug fixes that can resolve issues like freezing.
3)Export in Smaller Batches: Since you're exporting a large number of photos at once, try reducing the number of photos in each export batch. Start with 100 photos and see if that makes a difference.
Hopefully these solutions will work for you!