Hi
1. Your Radeon Pro 570x card is more than capable of running SimCity; the problem is due to being a legacy game, there is no code that recognizes updated / newer cards and systems. To fix, close SimCity. You will need to open the file ConfigManager.txt I'm not certain where this file is located on a Mac - it should be in a Config folder, nested under Applications/SimCity.app; the default location for this file on a PC is \Program Files (x86)\Origin Games\SimCity\SimCityData\Config
Make a copy of the ConfigManager.txt as a backup (just save it with a different name, like backupConfigManager.txt) Then open ConfigManager.txt with a text editor.
At the top, under Constants > set DefinitelyFail -3
Change the "3" to a "2"
# Constants
#
set Off 0
set On 1
set Min 0
set Low 1
set Medium 2
set High 3
set Ultra 4
set ModernFail -1
set ProbablyFail -2
set DefinitelyFail -3 Change the 3 to a 2
Save the file and try to launch the game again.
2. This issue sounds like a known problem with Mojave 10.14.4 and later. Please check this thread for more information and tips on fixing the problem. If it matches your issue, click the "Me Too" button and it can help to reply with the system information requested in the first post.
Let us know if this helps, or if you have further problems.
Happy Building!