How do live service games like Fortnite, COD Warzone and Forza Horizon 5 optimise their games for continuous content updates for wide variety of hardwares?

Sorry, I'm a complete illiterate on the tech side of things.

Do they just develop and test new content based on the lowest common denominator like the base Xbox One (Heard something like this because it's the weakest console so developers have to take that into account?) and then further optimise it to ensure stability across wide range of devices?

How can these games last so long on the base Xbox One and base PS4 and still can maintain a stable and playable frame rate?

With the exception of COD Warzone, both Forza Horizon 5 and Fortnite still looks so good and runs pretty well. Like what kind of black magic fuckery did they pulled off to make this work on such an ancient hardware?