Actually, Shenzhen is not very big, but most of the better-looking scenic spots are around Shenzhen. If there is only one day, it is recommended not to go too far.
In fact, there are still many places worth visiting in downtown Shenzhen, such as Civic Center, Shenzhen Bay Park, Lotus Hill Park, Ping An Financial Center, Dongmen Pedestrian Street, Garden Expo Park, OCT Creative Park, etc.
Shenzhen&;s subway and public transportation are very developed, and you can visit these places in one day.
Shenzhen is a new city. Urban buildings are planned in recent years, so they will be relatively new and tidy. If you want to find something more distinctive, you can visit Dapeng Lock City. It is the birthplace of Shenzhen.
You can also visit Ping An Financial Center and the roof. You can see all of Shenzhen in 360 degrees without dead angle.