This error appears on macOS during export (typically to Excel) and is related to the Zoom feature in Accessibility settings. It is caused by a conflict between Java and the system zoom feature, which results in a dialog window becoming blocked.
To verify this precisely, run Flexi with debug logs, in which you should find the following content:
How to resolve the issue:
Open System Preferences → Accessibility → Zoom
Adjust the settings:
disable the Zoom feature
or change its mode (e.g., do not use full-screen zoom)
Restart your computer
Summary:
The "RunModalForWindow" error is caused by the Zoom feature in macOS. Modifying or disabling this feature will resolve the issue.