@so0307 For this build, I'd change a couple things. First, two 8 GB RAM modules will give you significantly better performance than a single 16 GB stick. The motherboard can run memory in dual-channel mode, and doing so will make a big difference in certain tasks.
Second, I'd spend a little more money to get a higher-quality SSD, for example this one:
https://uk.pcpartpicker.com/product/zDhmP6/corsair-mp510-480-gb-m2-2280-nvme-solid-state-drive-cssd-f480gbmp510b
PCIe (as opposed to SATA) SSDs are significantly faster (around six times faster for Gen. 3 PCIe, which is what this motherboard uses), which won't make any real difference to Sims 4 but will make your system feel faster and more responsive overall. And they're cheap now, plus they're easier to install.
I do want to point out that 1 TB SSDs are cheap too, and if this computer is only for Sims 4 for now, dropping the HDD and going with a a single SSD might be the better solution. You could always add more storage later.
Finally, and most crucially of all, spend the extra money for a better power supply. If you get a bad one, or even one that's fine for a couple of years but starts to decay, it can and will affect your entire system. A bad PSU can even damage other components. This is the single most important decision you make when building a PC.
Corsair is the gold standard in PSUs, and Seasonic is the next-best option for those who don't want to pay for Corsair. EVGA is creating good PSUs too but hasn't been a big player in the market for as long, so I can't tell you that their products will last the way the others will. Corsair and Seasonic typically offer 10-year warranties, to give you an idea of how seriously they take this.
Given the components in this build, I think 80+ Bronze is good enough—it's not as power-efficient as Gold, but the components aren't power hogs and you won't be maxing them out with Sims 4. This is one good option:
https://uk.pcpartpicker.com/product/cY2bt6/corsair-cv650-650-w-80-bronze-certified-atx-power-supply-cp-9020236-na
Even though it's a little more expensive than the one you picked out, consider it an investment in the overall health of your computer.
The included CPU cooler should be sufficient for the processor as far as Sims 4 is concerned. If you upgrade to a faster GPU down the line, or start playing more CPU-heavy games, that's something to consider upgrading. But you can check the temperatures you're getting under heavy load and make the decision then; it shouldn't be a problem now.
By the way, the motherboard you picked out is ATX. That's a form factor, not a make or model.
I checked at least a dozen different U.K. sites for prebuilt gaming PCs, and I didn't find anything that was as good as what you've picked out in terms of hardware and price. The cheapest systems I found with a 3060 are these:
https://www.amazon.co.uk/ADMI-Gaming-PC-3000MHz-Windows/dp/B077GS751Z/
https://www.laptopsdirect.co.uk/cyberpowerpc-blaze-amd-ryzen-5-nvidia-geforce-rtx-3060-16gb-ram-1tb-ssd-win-ld22223/version.asp
Your build has a better processor, better storage options, and likely a better motherboard, although the product pages don't specify. The same goes for the PSU if you pick out a higher-quality option.
Downgrading to an RTX 3050, a GTX 1660 of some kind, or an AMD RX 6000-series only brings the price down to about £650. The 3060 is so much faster that if it's within your budget can accommodate it at all, I would definitely stick with it.
If you have more questions, feel free to keep asking.