Will it involve infringement to adapt a drama story into a novel?

No, fairy tales and folklore have no specific authors in the sense of copyright law, so there is no copyright. Even if there is, the term of copyright, in short, for individuals, is 50 years after death, while the term of spiritual rights such as the right of signature is infinite; For units and legal persons, it is fifty years after the first publication of the work.

For example, the crossing of the sea by the Eight Immortals you mentioned is a legend of the Ming Dynasty. Now, the copyright protection period has already passed.

Many traditional operas are born out of historical masterpieces, such as The Water Margin, a drama of the Three Kingdoms. In addition to infringement and non-infringement, these stories have been deeply rooted in people's hearts. It's nothing new to adapt it again. Unless it is changed to be like the ghost of a Chinese odyssey, it is completely decoupled from the fixed impression in people's hearts.