Short version: You can most likely start with a rig as weak as an I5-8400 and a 1050TI with 8GB DDR4 RAM and a SATA SSD. More computing power will be a benefit no matter which direction you go, except maybe text-based games.
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Longer version: The thing is, the game program itself can probably run quite easily on an I5-8400 and a 1050TI with 8GB of RAM. But how do you get the images you put in the game? Do you model them and render them? Because those programs tend to slurp up what they can get. An i9-11900 with a 4090TI and 64GB DDR5 RAM can Render far more than the previous config after all. They can both do it, but one might take 8 minutes where the other takes 40 seconds for the same render.
I think realistically, you'd probably want an i7-10700 with a 3060 and 16/32GB of DDR5/DDR4 RAM for good but not top of the line operating of the modeling software and the renderer. Once you have all the images and you only need to write code and put the .webp in the right spot you could probably do that from a cellphone, assuming Ren'py, RPGM or HTML. Unity is a bit heavier to run, Unreal even more so so those would benefit from the 10700+3060 over a cellphone.
If however you're not going for modeling and rendering, but instead real porn and you use photoshop and video editing? Both of those also heavily benefit from more computing power. So yes, you could probably run those on an 8th gen I5 with a 1050TI/2060. But every step up you can make in more cores, more speed per core, more graphics processing power, more RAM, working from an M.2 instead of a HDD etc. will improve how well and how fast the programs work.
Hope that was at all useful.
To give you very vague numbers, the 1050TI config would be about $1000, the 3060 config would be about $2000, the 4090TI config would be about $4000? So that's why I used those configs for the examples, they don't exactly need to be that, these aren't shopping lists, just examples.