The iconic Shibuya Square fills with people at all times of the day, so how is it possible to empty such a place? Did the shooting take place on a holiday? During the confinement? Did they cut off all access for a few hours?
Neither of these assumptions is correct as Shibuya is very crowded even on holidays and there have been no blockages in Japan. The closure of the plaza would not have been possible because it would have impacted too many people. The only solution left for the producers was to simply build Shibuya! Therefore, an identical replica of the street was created. Then with special effects, they added the buildings to make a perfect illusion.
While we wait for season 2 of Alice In Borderland, we recommend the making-of where the actors and the creator review the staging of the series.