No matter whether it is public or not, you can't protect it with a patent, because when you apply for a patent, your own technology has been made public, so there is no trade secret. If there is, you can't sue with patents, you can only rely on contracts to safeguard your own interests.
Article 59 of China's Patent Law stipulates: "The scope of patent protection shall be subject to the contents of its claims, and the description and drawings can be used to illustrate the claims." However, if the scope of protection is determined strictly according to the technical features recorded in the claims, it will often bring unfair results. That is, when the patentee applies for a patent, it is difficult to predict all possible forms of infringement and record them in the patent claim. In some cases, it is even impossible. For example, the replacement between natural rubber and artificial rubber seems easy now, but in the era of only natural rubber, it is impossible to record artificial rubber in claims.