Historical-Era or Modern Urban Stories Where the Protagonist Can Transmigrate Between Two Parallel Worlds 年代文 现代都市 主角可以两个平行世界穿越的

The protagonist can transmigrate from the modern world to the late 20th century, freely traveling between two parallel worlds and living and developing in both. Or they can transmigrate from the late 20th century to the modern world. Either way, I want them to be able to travel back and forth between the parallel worlds and make use of the resources in both.