I think the system requirements for Rare's Sea of Thieves is a shining example of how system requirements should look.
The game's system requirements clearly detail the hardware required to run the game at the given settings, resolution and the frame rate target, it's fantastic!
It's very well communicated with the players and provides a solid basis for people to pick some settings for the game and then tweak from there should they desire to do so.
In-game comparisons of the visual differences is great to see in PC games, and indicators of the performance impacts of the settings is very important too!
I think it would also be great to see PC games offering settings equivalent to a particular console (providing there is a console version), so people can use those settings and scale up or down from there.
Clearly communicating the system requirements is important, this should help temper expectations and reduce the likelihood of misunderstandings regarding a game's performance, in a time when people will moan first and ask questions later.
Durante made an article on PC Gamer about optimization in games, in this article he uses Dying Light as an example of a game where people complained about the performance because they cranked up a draw distance setting and were unsatisfied with the performance, what they didn't know is that this setting goes well beyond the console versions of the game and was tailored specifically for PC Gamers.
PC Gamer: What 'optimization' really means in games
Red Dead Redemption 2 has an extensive list of settings, but you don't really know how much of a performance impact they will have until you try them.
This is how PC Gaming has been for quite some time, but I would argue that more recent games have taken a better approach to presenting options to the user, an example of a game would be Gears of War 4 and 5. These games have extensive settings lists too! However, they present them in a way that is very well communicated with the user, by detailing what hardware it stresses and by how much and even showcasing the visual differences of them in Gears 5!
Gears of War 5 - Screen Space Reflections example: