If you are thinking of upgrading to the new macOS Catalina (10.15) and want to use ChimeraX on it you might hold off.
We have found that opening files using the ChimeraX open command or the recent files thumbnails often causes PermissionError and fails to open the files. This is caused by a new macOS Catalina security feature when any app that tries to open a file under Desktop, Downloads, or Documents must first raise a permission dialog asking if the app is allowed to open files from that directory. When using the ChimeraX File / Open dialog (from the File menu) the permission dialog is shown and works. But if you use the ChimeraX open command of recent files thumbnails on directories that you have not granted permission for with the Open dialog, then those fail with PermissionError -- apparently those methods of opening are not able to show the permission dialog.
Other applications (e.g. photo editing program Gimp) have the same problem. We do not yet know how to solve this.
Tom