Is it still considered disbelief to believe in a sorcerer's ability to perform magic without using a physical trace, after having learned about the possibility of magic being done through voice or by using a person's name and their mother's name? And is researching this considered a sin?

We do not have definitive information regarding how sorcery occurs and how it takes effect. Nor do we know of any detailed basis for it in the Sharia (definition) that can be relied upon for negation or affirmation. In matters of the unseen, one must rely solely on the textual evidence. As for researching these issues, there is no harm in it, but it is better to occupy oneself with the texts of the two revelations (Quran and Sunnah (definition)), fiqh (Islamic jurisprudence), and tawhid (definition) (monotheism), and not to be preoccupied with matters from which there is no benefit in learning.