Game will not open on Mac (in need of desperate help!)

Please try this:

1. Drag your whole Sims 4 folder from Document > Electronic Arts to your desktop.
2. Launch Sims 4. You should get no list of mods on launch, and you should have no option to load a previous save. Reset your Options.
3. Start with New to make a test save.
4. Now go freshly download one piece of recent CC, install in the new Mods folder, and try the new save. 

If that works, you can start putting mods back, but do check for ones known to be broken, and do it in batches.