Is it correct to say that "if only" (لو) opens the doors to Satan, even though it appears in the Noble Qur'an, such as in His Almighty saying: {Say, "If the sea were ink for the words of my Lord, the sea would surely be exhausted"}?

"Law" (لو) carries multiple meanings, and its utterance is not always forbidden. Indeed, Al-Bukhari dedicated chapters to its permissibility in certain contexts. The prohibition mentioned in the Muslim حديث (hadith (definition)) is understood to apply when it is used to express lamentation over worldly matters, or to object to divine decree, or when there is a lack of reliance on Allah, or when depending on means without considering divine predetermination, or when expressing displeasure with it. However, "law" (لو) is permissible after a decree has occurred, and it can be used to express a wish for acts of obedience. It may also mean "in" (إن) or "hala" (هلا - meaning 'why not' or 'if only'), or it can be used for minimization, as found in the Quran and in the speech of the Companions and the Salaf.