First of all, right-click on your desktop and select 'New' -> 'Folder'
Create a folder and name it something to distinguish it (say SI backup)
Once you've done this go to your Sports Interactive folder found within 'documents' which by default is at the following location - \Users\[YOUR Mac USERNAME]\Documents\Sports Interactive\Football Manager 2019
This should contain folders like 'games', 'crash dumps' etc. Please cut every folder from here and paste them into the folder you've created on your desktop.
Once you've done this and the Sports Interactive\Football Manager 2019 folder is now empty, launch the game. If it works, copy back the files from the desktop folder and hopefully it should now load without any issues.