@Michel B You want the app to work in the current version of Catalina, and unfortunately, 2019R1.1 don't support launching other apps.
2019R2 is probably not that far away, which should alleviate the issue.
Have you tried the MBS Launch Services functions?
I've just ran quick test remote debugging the following code from my Mac running Xojo 2017r3 to an iMac running Catalina beta 5 and it successfully opened a screen shot in Safari.
Dim applicationFolderItem As FolderItem Dim documentsList(-1) As FolderItem Dim launchServicesParamsObj As LaunchServicesLaunchParameterMBS Dim result As FolderItem 'find the application applicationFolderItem = SpecialFolder.Applications.Child("Safari.app") 'add our document to the list we want to open documentsList.Append(SpecialFolder.Desktop.Child("Screenshot 2019-06-05 at 10.43.31.png")) 'define the launch parameters launchServicesParamsObj = New LaunchServicesLaunchParameterMBS launchServicesParamsObj.Defaults = True launchServicesParamsObj.Application = applicationFolderItem 'launch result = LaunchServicesOpenXMBS(documentsList, launchServicesParamsObj) Break