@RoseFinn12 Okay, these sites provide some good examples of your options. Please keep in mind that prices can change quite a lot in a short amount of time, and stock turns over quickly, so these exact models and the various configuration options probably won't be the best choices for you when you're ready to buy. This is more about showing how the process would work in general and what your new computer might cost.
To start with, this is an expensive (16.299 SEK) example of a system that's overpowered for Sims 4, by a wide margin, and would accommodate almost any graphics card currently on the market. (The $1,600 RTX 4090 would need more power, but that's a ridiculous GPU anyway.) It has all high-quality components, the kind you'd buy if you were building the computer yourself, although I'd personally prefer a better CPU cooler. You're also paying a premium for the company to build it for you.
https://sharkgaming.se/ktg-serious-pc-v3
In comparison, these two are typical prebuilt computers with similar hardware: processors that are less powerful but still more than good enough, and less storage. The HP uses generic components manufactured for HP, so upgrade options would be somewhat limited; you could easily add storage and RAM, but the low-end power supply and the motherboard's proprietary connections mean it would be difficult or impossible to make any other improvements. The Lenovo build uses higher-quality components that can be swapped if necessary, but you'd still need a new power supply if you upgraded the graphics card.
https://www.komplett.se/product/1180988/gaming/gamingdator/gamingdator-stationar/hp-pavilion-gaming-tg01-2027no
https://www.inet.se/produkt/2219182/lenovo-legion-t5-i5-16gb-512gb-rtx-3060-ti
On the other hand, if this computer only needs to last around five years, the Lenovo would be an excellent choice. A 3060 ti is always going to handle Sims 4 without any trouble, and whatever Sims 5 turns out to be, this GPU should be more than fast enough for the first couple years. Sims 3 and 4 were comparatively easy on hardware in the beginning and only became more demanding with the release of Pets/Cats & Dogs and Seasons, so if Sims 5 followed that pattern, you wouldn't need to worry about upgrades for a while.
If you do want to set up the computer so it can be easily upgraded as you go along, Shark Gaming looks like the better option right now in terms of price and selection, although like I said, things can change over time. As an example, you could start with this model:
https://sharkgaming.se/shark-bloodlust
Upgrading the processor to an i5-12600KF costs 1.040 and also gives you a CPU that would support whatever graphics card you want in the future. It would also easily handle a heavy load of simulation-related calculations. This is the kind of processor that can handle any current game regardless of settings. I'd definitely upgrade the cooling, maybe to one of the Noctua options (+69 or more) at possibly to the Arctic liquid cooler (+479) at the high end, but I'd need to look at some benchmarks.
For the rest of the build, I'd upgrade the power supply to the 850W Hydro K Pro (free) or perhaps something better and a bit more expensive if it's available at the time. (The Hydro performs well but is a bit loud, and I personally would gladly pay more for a premium brand like Corsair.) This particular 3060 isn't the best version, but I would only worry about it if you were going to run it close to full load, which you're not because Sims 4 can't come close to maxing it out. (I've benchmarked the game on a 2070, which is quite similar in terms of performance, so I know.) When the time came for a better GPU, maybe three or four years down the road, you could pick the card you wanted without changing anything else.
There are also AMD-based builds that might be more cost-effective, depending on which components you want. For example, this one is 13.940 with a Ryzen 5 5600X and an Asus Dual 2060 (or +600 for a Dual 3060), plus the cheapest Noctua cooler. (Noctua is the gold standard in CPU air coolers and has been for a while.)
https://sharkgaming.se/max-bite-predator-v2
When you're ready to buy, feel free to come back for help choosing a build, or just to have someone look over what you've already selected. And if you have more questions now, please keep asking.