@AlexvonAuen I'll start with the easy part first: UserBenchmark is not a reliable source of information. The Nvidia 40-series in general has also received a lot of criticism for pricing, most of which is valid but doesn't say anything useful about performance. A GPU that's a disappointment at $800 might be an excellent option at $600.
The two models you're looking at appear to be built like laptops in that everything is soldered to the motherboard. That's fine if you're comfortable with it, but I wanted to mention it given your concerns about the repairability of laptops in general. These models don't have as many failure points since they don't come with a built-in screen, but you're still stuck with soldered components.
I'm not surprised that the 4070 model is cheaper. The GPU isn't much faster than a 3080 at its best, and can be slower in some workloads, plus as you noticed, the sentiment around the 4070 is such that it's not selling as well as the last-generation chips. The difference in memory is just what the processors and chipsets support: Intel didn't introduce DDR5 support until 12th-gen, so the i7-11800H is stuck with DDR4 and its comparatively slower speeds. This would be noticeable in benchmarks but won't have much of a practical effect, and probably none in Sims 4.
Having said that, both of these are massive overkill for Sims 4. The game won't come close to maxing out the hardware in either case. That doesn't mean you wouldn't get any lag—Sims 4 will have slowdowns on any system due to how it's programmed. But it won't be the fault of the components. That would be true for a 4060 or 3060 ti too, even playing at 4k.
I can't really tell you how Life By You is going to run this far out. My understanding is it's quite demanding but also not yet optimized, which basically means we know nothing useful at this point. I will say that given the target audience, the developers would be foolish to require more than, say, an RTX 3060 or so even for ultra settings.
If you want a small form factor desktop PC, there aren't many options out there that include proper desktop hardware without a desktop-sized case. You might consider an Intel NUC though. They can be expensive, but they also use standard components, meaning you could upgrade or replace almost anything without worrying about repairs. But if the laptop-style build of the Zotac options doesn't bother you, it's certainly a reasonable choice.
