Hi,
We're sorry about the trouble while trying to launch Lightroom Classic. Would you mind telling us the version of Lightroom Classic insatlled on the machine?
Please ensure that Lightroom Classic has the necessary permissions on macOS by following the below mentioned steps:
1. Go to the System Preferences for your Mac, then Security and Privacy, then select the Privacy tab.
2. Then select Accessibility from the list to the left & check if Lightroom Classic is added to the list with a check mark in front of it.
3. If Lightroom Classic is not a part of the list, please add it by unlocking the window first using the lock at the bottom left, then clicking the + icon & navigating to the Applications folder.
4. Also, grant permissions to Lightroom Classic under Full disk access located in the same list as Accessibility.
5. Once done, restart the Mac & check if it helps.
If the issue persists, you can try to reset the preferences of Lightroom using the steps mentioned here: https://adobe.ly/2JSym5e
Please backup your presets prior to resetting the preferences.
Let us know how it goes!
Regards,
Nikunj