OK Dan,
Sorry for the delay. I have been able to run through your actions and can report the following:
Are you able to use File > Save As as expected, or do you see the same behaviour as when exporting?
Are you unable to export to any location on your Mac, or does this hang only happen when exporting to a specific location? for example can you export to your Desktop, or does this also hang?
I cannot save a file to any location using Save As, or Export. Sometimes It freezes and I have to restart. Once or twice it saved an image but it would not let me change the same (it froze when I tried). I have sent an error report if one came up to be sent.
If you open macOS System Preferences > Security & Privacy > Privacy > Files and Folders does Affinity Photo appear in this list?
How about macOS System Preferences > Security & Privacy > Privacy > Full Disk Access? Affinity Photo does not appear on either list. Should it?
Marjorie