The usual culprits for symptoms like these are antivirus, anti-malware, or permissions on the folders. Make sure that you haven't put password protection on any of the SimCity files or folders, and that SimCity and Origin are marked as exceptions in your firewall and anti-virus.
If you continue to have issues, please reply back and provide more information about your iMac. Instructions on how to do so here - https://answers.ea.com/t5/The-Sims-Mac/READ-FIRST-Sims-4-Mac-Help-Guides-and-Troubleshooting/m-p/4612396/highlight/true#M162 Did you purchase from EA through Origin or from Aspyr through the App Store? Also, let us know if there are any error messages, or if the program is just stalling at these particular points. A screen shot of any error messages could be helpful, too.