@natasha88138689 , try moving the entire Sims 4 folder (Documents > Electronic Arts > Sims 4) to your Desktop and do NOT delete it! This is where your saved games are store. Next start up the game to see if it still stuck at loading the game. The game will regenerate a new Sims 4 folder. If your game loads and comes to the starting menu, remember that none of your saved games, CC or mods will be present at this time. Start up a new game to see if the game starts correctly and that there are no other issues present at this time. Play for about an hour and quit the game.
If the game started up ok and played ok, then it is probably a mod that is out of date or a piece of CC that is either a very high poly count or out of date as well. Before adding any mods back, check the sites you downloaded them from and make sure that they have been updated to work with the latest patched version of the game. (Last patch was dated 12/20/2018). Once you have insured you have the latest versions, add each mod back one at a time, start up the game and make sure that it loads and starts up correctly. Repeat this process until you have added all your mods back and verified that they all work and your game starts and plays without issues. Same with your CC. You can add back a few pieces at a time (I recommend no more than 10), start your game and verify that all is working ok. Unfortunately there is no program written for the Mac OS that will check your CC for "bad" content. You will manually have to cull your CC by hand.
If this does not solve your problems, please post your Mac Specs here. Do not post your Serial Number! Here is the link on how to find that information if you need to do so.
https://answers.ea.com/t5/The-Sims-Mac/READ-FIRST-Sims-3-Mac-Help-Guides-and-Troubleshooting/m-p/749664#M3
Please keep us posted.