Singular: referring to the greatest sin (shirk). It may also be intended in the plural meaning.
خَطِيئَاتُهُ
khaṭīʾātuhū
“and his sins have encircled him”
I.e., the major sins, the biggest of which is disbelief, (or a reference to the many punishments of his great sin).
Explication
These readings amount to the same meaning, as the concept of 'encircling' implies plurality. In both readings, the word khaṭīʾah appears after the similar term sayyiʾah, and one or the other may refer to major or minor sins, or specifically to the greatest of all sins, i.e. associating partners with Allah [Makki].
He has revealed to you ˹O Prophet˺ the Book in truth, confirming what came before it, as He revealed the Torah and the Gospel
Explication
These readings amount to the same meaning, as the concept of 'encircling' implies plurality. In both readings, the word khaṭīʾah appears after the similar term sayyiʾah, and one or the other may refer to major or minor sins, or specifically to the greatest of all sins, i.e. associating partners with Allah [Makki].