@mrsalynn There aren't many great options for $600, although if your total budge is $950, you could spend a bit more and save on the monitor. There are good monitor options in the $100-150 range, especially if you're fine with a 1920x1080 screen. For the desktop itself, this is the cheapest good option I found, at $600:
https://www.bestbuy.com/site/cyberpowerpc-gaming-desktop-amd-ryzen-3-2300x-8gb-memory-amd-radeon-rx-570-1tb-hdd-240gb-ssd-black/6362425.p?skuId=6362425
Its processor isn't that strong, but it's still good enough for Sims 4; its graphics card should run the entire game on ultra settings.
This one is $650 and has a significantly stronger processor, but a somewhat slower graphics card. The Nvidia 1650 is still capable of maintaining ultra graphics settings though. The major disadvantage of this option is that it only has a slow mechanical hard drive, so everything from Windows to Sims 4 would load more slowly. The game would run the same once loaded though.
https://store.hp.com/us/en/pdp/hp-pavilion-gaming-desktop-tg01-0170m-7bb49av-1
These two are $750 and have similar specs. The Nvidia 1650 Super is a bit faster than the AMD RX 580; the Ryzen 5 3600 is a bit faster (in gaming) than the Intel i5-9400F. They're both excellent systems. The quality of iBuyPower builds isn't always great, but that's why you get it from Best Buy and not online.
https://www.bestbuy.com/site/cyberpowerpc-gaming-desktop-amd-ryzen-5-3600-8gb-memory-amd-radeon-rx-580-2tb-hdd-240gb-ssd-black/6362427.p?skuId=6362427
https://www.bestbuy.com/site/ibuypower-gaming-desktop-intel-core-i5-9400f-8gb-memory-nvidia-geforce-gtx-1650-super-1tb-hdd-240gb-ssd-black/6400463.p?skuId=6400463
As for monitors, there are too many options to list without knowing your preferences. These two are cheap and good quality though. IPS is the best category in terms of color, and both Asus and Dell make high quality monitors. The 75 Hz refresh rate of the Asus would make a difference to some people, but not to others; your Apple screen is 60 Hz.
https://www.amazon.com/ASUS-VA24EHE-Monitor-1920x1080-D-Sub/dp/B07Z8TC28F/
https://www.amazon.com/Dell-SE2419Hx-23-8-1920x1080-Monitor/dp/B07HKV5RLG/
Let me know what you'd like in a monitor, and I can look more. You probably won't find many options from good manufacturers that are cheaper than these though.