I ran “Activity Monitor” while Exporting.
I have no idea what “XPCCor1” is or does, but when I’m not using PL5, its CPU is 0 %
While Exporting I got this:
I thought I saw it up to over 600. And when Exporting finished:
I have no idea if this is a useful clue. However, this link mentioned it for an earlier version of macOS:
https://forum.dxo.com/t/dxo-photolab-2-3-1-b43-export-doesnt-work/9420