In this reading, al-ākhirah is nominative as an adjective.
وَلَدَارُ الآخِرَةِ
wa-la-dāru l-ākhirati
“the abode of the final (life)”
In this reading, al-ākhirah is genitive due to annexation (iḍāfah). It may be considered as an adjective for an implied word.
توضیح
These readings amount to the same meaning, especially if the annexation in Ibn ʿĀmir’s reading (which accords with the Levantine Codex with single lām) is taken to be descriptive [al-Alusi].
He has revealed to you ˹O Prophet˺ the Book in truth, confirming what came before it, as He revealed the Torah and the Gospel
توضیح
These readings amount to the same meaning, especially if the annexation in Ibn ʿĀmir’s reading (which accords with the Levantine Codex with single lām) is taken to be descriptive [al-Alusi].