The Aramaic Job targum from Qumran ends early and differs from the Hebrew in places. A translation isn’t evidence for the stability of the Hebrew text.

The targum is evidence that Job was valued and read, which is what it is cited for. For textual stability the Hebrew fragments (4QJob-a and 4QpaleoJob) are the relevant witnesses, and they align with the Masoretic tradition. The targum’s differences and early ending are interesting for the history of interpretation and should not be counted toward the stability claim.