Thanks Quinn. It certainly looks like this is the same bug (or feature) which the other threads are reporting. I'll do as you suggest and run 26.0 in a VM to see if that also has the same problem.

This is on 26.1 More information: I updated my own Mac from 15.7 to 26.1. The accessibility settings for my app seem to have been carried over from 15.7 to 26.1. The difference being that the app is no longer listed in the accessibility window, even though the functionality remains. It is several customers who are having the problem, all with fresh installs of 26.1 Thanks for the link to the other thread. It seems to relate to Full Disk Access but maybe the Accessibility is compromised in the same way with 26.1. That might explain why I've had no customers complain about the bug with 26.0 I have tried to get my Mac into the same state to help with debug but even running the command line tool to remove the accessibility option from ALL apps still leaves my executable working!