The phrase "in an unknown manner" can be replaced with a number of synonyms to add more specificity to the idea. Some options might include "in a mysterious way," "in an obscure manner," "in a cryptic fashion," or "in an enigmatic style." Additionally, one could use phrases like "unfathomably" or "unpredictably" to describe the unknown nature of something. No matter which phrase is chosen, the goal is to convey something that is ambiguous or difficult to understand in a way that captures the essence of its mysteriousness. Ultimately, the right synonym for "in an unknown manner" will depend on the context and intended tone of the writing.