For the record: This problem has gone away under Ventura. Same app, same installer, same entitlements... and the applescripts run just fine on Ventura. So I'm guessing it became a known issue and nobody wanted to fix it on Monterey.

My solution: Issue was with adding/removing new lines being reeeeeeeeeealy slow (like 2 second delay after hitting ENTER) It's is helped massively by closing all other open tabs. Obviously this is a pretty lame solution as the tabs are really handy.

me too. Specifically enter/delete to add/remove new empty lines is really slow

Same problem here. I'm just trying to call a menu item in another app. Testing on Monterey 12.3.1. Running NSAppleScript::executeAndReturnError. I've set NSAppleEventsUsageDescription. I've got the entitlement com.apple.security.automation.apple-events. I've also got com.apple.security.temporary-exception.apple-events for the target app. I'm successfully notarised and installer is stapled. This thread is enlightening but I still can't run an AppleScript. https://stackoverflow.com/questions/70548909/how-to-run-applescript-from-c-in-macos-sandbox-environment-without-entitlement