Planning a living world as a DM

I've just finished watching The Fantasy Forge's video about adding small worldbuilding details to make the world feel alive, I'll also add the link at the end for you to see exactly what I'm talking about. Now, I've been DMing on and off for years now, but never really built a world for a campaign myself.

What I'm not sure about is how prepared in advance I should think of those things, I feel like thinking of regional sayings, superstitions, local heros and more, for some of my different regions and cities will be extremely time consuming and require a ton of thought, and for tips that stem from a video about adding tiny details it seems too much.

What I wanted to ask is for some tips from DM's that use similar stuff in their worlds, and ask how exactly do you prepare it. And if some of you have some general tips for making a world feel alive, with history and culture, and also explain how do you prepare those stuff while building the world.

The link to the video I was referring to - https://youtu.be/cHyzZmfawU4?si=zRLMGn94d8AqRpJB