After some more testing today, I can also confirm that if I remove the "app sandbox" from the app "signing & capabilities", it works. However, with the app sandbox enabled, it does not, even with both: com.apple.security.files.user-selected.read-write and com.apple.security.files.user-selected.executable set to true (enabled)... While I still have the problem, this seems to be isolating the issue to the "app sandbox" settings. Any help with that would be graciously appreciated.

The app uses the "Process" class to run Bash shell commands, allowing it to execute commands that can be run in "Terminal". After I make the script, I do make it executable, and I can run it directly from Terminal. The scripts are located on the file system, not inside the app bundle, my guess is that this has something to do with the problem - or the problem is caused by the permissions to interact with another app (in general, the sandbox settings). I mentioned the error above.