Tafsir of Al-Burooj 85:20

It is permissible for this to be a parenthetical statement serving as a conclusion (tadhil), or a circumstantial qualifier (hal) related to the pronoun in the preceding prepositional phrase. The statement is an analogy for the impossibility of them escaping the might of Allah Almighty, just as an encompassed object cannot escape the encompasser, as stated by more than one scholar.

The meaning is that He, Exalted and Majestic, is knowledgeable of them and powerful over them; they cannot frustrate Him, nor can they escape Him—Glory be to Him and Exalted is He.

‘Isam al-Din mentioned that this contains a substitution and a rebuke to the disbelievers for having cast Allah behind their backs and turned themselves entirely toward desire and lusts. Perhaps this is the reason for shifting from the pronoun "them" (bihim) to "from behind them" (min wara'ihim).