Are all verses in the Qur’an connected to the ones preceding them, or can a new topic begin within the surah, or is there a hidden connection that links the verses of a single surah?

If the intended meaning is the connection of verses in terms of subject matter or meaning, then this is not necessary, as many verses address a different topic. Nevertheless, the totality of the Quranic verses has a connection with those preceding them, whether apparent or subtle. Scholars have authored books on this subject, most notably Imam Al-Suyuti in "Al-Itqan" in the sixty-second type concerning the suitability of verses and surahs.