Is it true what is mentioned in books of Tafsir that "Qaf" is a mountain that surrounds the entire Earth, given that there is no mountain surrounding the Earth?

The statement that (Qaf) is a mountain surrounding the earth is false, and there is no evidence for it in the Qur'an or Sunnah. It is among the Isra'iliyyat (tales of Jewish origin) and superstitions that have no basis. The correct view is that (Qaf) is an alphabetic letter used to open some surahs, like other disconnected letters. If it were a mountain, it would have been written as "Qaaf" (قاف) not "Qaf" (ق).