I have exactly the same issue and I am convinced it is a bug with either Macs or the M4 specifically. You will find some options for trying to fix it here in the forum, but in my case, they have not worked. I hope the developers see these forums and see there is a problem and work to fix it. To get out of the loading screen, you can Command + Tab to switch to another screen and then select your apple icon in the top left corner. Select 'Force Quit ...' and then choose Sims 4. I have managed to get some game play by enabling vsync (just search for that here in the forum and you will find instructions) and playing in offline mode. However, when coming out of creating a sim or switching to another location on the map, the loading screen often hangs, at which point I use the force quit option and restart the game. I have learned to save before I go into different modes. This is an absolute pain I know so I hope this is fixed at some point in the future!