When crossing a street and waiting for the traffic lights, it's common that many people would look down while swiping their smartphones.

When waiting at a traffic light, it's common for people to be on their phone.

I guess this can be an attractive project to invest in.

This might be a valuable project for someone to take a look at.

When crossing a street and waiting for theat traffic lights, it's common that to cross a street, many people wouldcommonly look down while swiping on their smartphones.

"Swipe" also means to slide something through something else, so the original sentence might cause a bit of confusion to less tech-savvy people.

Is it possible to createestablish a special zone in a metropolitan where area/city where there's no Internet connectivity and the use of digital devices are noisn't allowed and the internet would also be cut off?

This would make the sentence sound even better and fluent. However, there are more apt words you can use to describe several concepts in your sentence. Here's an example sentence that conveys the same meaning:

Would it be feasible to establish a designated area in a metropolitan city where digital devices are prohibited and internet access is restricted?

I guessbelieve this canould be an attractive project to invest in.

"I guess" makes it sound like you're highly skeptical. It's your idea so it might be better to use "believe" instead.

An even better way of saying this is:

I believe this could be a promising investment opportunity.

People who stay iIn this special area, which I nam'd like to call the "Digital Detox Zone," people would only be allowed to watch TV, listen to the radio, and chat with each other face-to-face.

I rewrote the first part to improve the readability and flow of the sentence. You can also use "converse" instead of "chat"

Probably,erhaps only rich people who would likeilling to pay, or people with diagnosed digital addictions who got(and possessing a doctor's prescription can be able) would be allowed to enter the zone to relax.

I rewrote a lot of the sentence, but the original sentence also conveys the message with a few grammatical errors.