Need help finding new desktop !

I didn't see your comment before I went to bed, so sorry for the late reply. $800 U.S. is absolutely doable; in fact, you could go under and still get a good enough computer.

This is the lowest I'd go—its graphics card, an AMD RX 580 4 GB, is the minimum you'd need to ensure you can always run all packs on ultra settings. It has a very good processor and a 500 GB solid state drive; SSDs are much faster than HDDs, which won't make a difference for TS4 but will make any TS3 loading (entering CAS or Build/Buy, loading saves, traveling, using Edit Town) much faster, and Windows will run a lot more quickly as well. It's $635.
https://www.amazon.com/SkyTech-Archangel-Gaming-Computer-Desktop/dp/B07JYF2394

These two have stronger graphics cards but otherwise the same hardware as the one above. The Nvidia 1660 is a bit more power than you need, but you might want it if you really like using high poly custom content (the detailed, harder to render items) in TS4. The 1660 ti is even a bit stronger than that, definitely more than necessary. The models are $750 and $800, respectively.
https://www.amazon.com/SkyTech-Blaze-Gaming-Computer-Desktop/dp/B07RHBLV7F
https://www.amazon.com/SkyTech-Blaze-Gaming-Computer-Desktop/dp/B07RL4K6CN

All of these models only have 8 GB RAM, which is enough to play either game but maybe not for much multitasking. (For example, music or a browser window would be fine; editing your screenshots while playing might be pushing it.) But it's easy enough to add another identical RAM stick if and when you need it. You should be able to find one for $50-60 on Amazon, once you know the model number in the computer, and installing it is simple.

The reason these computers are so cheap is that their other parts (power supply, motherboard, CPU cooler) are the minimum necessary for the rest of the hardware. That's fine if you just want the computer to run as is and aren't interested in upgrades. If you do want to upgrade later, or at least want the option, I can find some models that would make that easier. Of course, they'll be a bit more expensive.

Anyway, these models will all handle TS3 and TS4 just fine. If you have any questions or want more details, feel free to ask.

@puzzlezaddict thank you so much !! could you recommend a monitor for the $800 option you gave me?

Honestly, I'm not good at all with monitors. In terms of categories, IPS has the best color range, and TN is nowhere near as good. But TN panels offer high refresh rates for much less money, so they're favored by gamers who want that 144 Hz (frames per second) to better mow down enemies in Battlefield or whatever. Playing Sims games, you might not notice a difference between 60 and 144 Hz, or if you do, 75 Hz might be a good compromise. Another compromise to consider is the VA panel, the best of which look almost as good as IPS monitors but are still cheaper, and the more expensive ones have refresh rates comparable to TN panels.

A big part of it is your own personal preference. For example, Dell monitors are reliable and generally high quality, but I personally don't like how they look and would never buy one for myself. The best favor you can do for yourself is to go to a Best Buy or similar store and just look at the screens, and think about how it would feel to use them. You don't need to see a wide selection—all screens of a particular type made by a particular company (i.e. Samsung VA panels) will look the same. Sit in front of the different size screens too; so you know what you'd like. Once you have a list of companies you'd be willing to buy from, you can check online (Best Buy, Amazon, Fry's, etc.) to find the best price.

@FloridaSimmer I looked at Amazon again, as well as Skytech's product pages, and I think the best option is the second one listed. The first one, as it turns out, has much slower memory than the others, for no discernible reason. AMD processors are particularly sensitive to RAM speed, so there might be a noticeable impact on performance, when doing other tasks if not gaming.

The Blaze II with the Nvidia 1660 will run all of TS3 and TS4, plus your cc, plus all TS4 packs that haven't yet been released, on ultra settings. It's still $750, and although it's out of stock, it's supposed to be back in within a few days.
https://www.amazon.com/SkyTech-Blaze-Gaming-Computer-Desktop/dp/B07RHBLV7F

This is Skytech's product page, if you're curious, but it's a bit more expensive there than on Amazon:
https://skytechgaming.com/product/blaze-ii-amd-ryzen-5-2600-nvidia-gtx-6gb-gddr5-500gb-ssd-8gb-ram/

If you did want a stronger graphics card for other games—neither TS3 nor TS4 would benefit—the next higher Blaze is still the best option as well. It's $830 now on both Amazon and Skytech's own site.
https://www.amazon.com/SkyTech-Blaze-Gaming-Computer-Desktop/dp/B07RL4K6CN
https://skytechgaming.com/product/blaze-ii-amd-ryzen-5-2600-nvidia-gtx-6gb-gddr6-500gb-ssd-8gb-ram/

You may want to add more memory to the computer, now or later. This is simple: take the front panel off and check the serial number on the existing RAM stick (or you might find it listed in the manual), and order an identical 1x8 GB stick. It might only cost you $40 on Amazon, given current prices.

@puzzlezaddict is that desktop still good to buy ? I finally am able to purchase a desktop but is it still the best on the market?