What is the difference between "فَمَا اسْطَاعُوا" and "وَمَا اسْتَطَاعُوا" in Surat Al-Kahf?

The exegetes (mufassirun) mentioned two aspects concerning the difference between "istatā‘ū" (استطاعوا) and "ista‘ū" (اسطاعوا):

The first: It is a lexical difference intended for rhetorical variation and to avoid repeating the same word.

The second: It is a semantic difference, where the increase in structure indicates an increase in meaning. Thus, "istatā‘" (استطاع) with the letter tā’ (ت) denotes a stronger and more intense ability, whereas "ista‘" (اسطاع) with the omission of the tā’ denotes a lighter ability. This is consistent with the context of the verses in the stories of Moses and Dhul-Qarnayn.