What is the reason for the raising of the word "laghāfilūn" in verse 92 of Surat Yunus, even though it is preceded by "al-lām" which appears to be a preposition, and is the lām here not for preposing?

The aforementioned "lam" is not a preposition (harf jarr); rather, it is the lam of emphasis (lam al-ibtida'), which accompanies the predicate (khabar) of "inna" (with a kasra on the hamza) for emphasis and is pronounced with a fatḥa. This is in contrast to the lam of a preposition (lam al-jarr), which is pronounced with a kasra, except when it is attached to a pronoun. Thus, "ghāfilūn" is the predicate of "inna," and "kathīran" is the noun (ism) of "inna."