vfx Period Films Street Scenes

I watched Once Upon a Time in Hollywood yesterday. There are a lot of street scenes (characters driving in cars in many scenes, characters walking on streets, etc.) that resembled the 1960s, the story that took place. Did they shoot the street scenes as of today, and did they went back and changed each and every building in CGI to simulate the 1960s? Or at this point, are there any templates of 1960s street that can be used a background, and they just shot what they need and merged into it?

PS: Normally the other period films I have watched, for example, Once Upon a Time in America, they build a few street sets, but they kept on milking that set. But Once Upon a Time in Hollywood was all over the place.
I'm not a visuals type by any means; my specialty is audio. But my understanding is that, for quite a few of the well budgeted projects, they build "half" sets; the immediate street(s), etc with which the characters interact and the rest is CGI. As an example, Ridley Scott used this method in "Gladiator" for the Colosseum scenes - they built one half of the lower tier of the Colosseum and CGI does the rest. Even many TV shows set the in the present use CGI to enhance their scenes.

I hope that others more qualified will respond
Well, he's Tarantino. He says "this is what I want to do." and everyone knows that the odds are it will be something extraordinary, so the higher ups say "Okay." The advantages of being a living legend.