I don't think its outright claimed that Jews are corrupted but just an observation and logical assumption we make because of other realities.

The terminology is another subject within itself. Foremost, Jews were Muslims. All nations were sent Prophets but the Prophet Muhammad comes from one of those nations and it just so happens to be related to the Jews, as Arabs are Semitic.

These Jews obviously received guidance from their Prophets throughout time, such as other nations of Humans were.

Their message was not preserved. Also its said that in general, the Jews who reject Islam have become corrupt due to their ties to their family and tradition. Give it up. The Jews and Christians care more for their emotional attachment to their traditions than the reality that the Prophet Muhammad was the final Prophet of Allah subhanahu wa tala.

The Message the Prophet Muhammad was sent by Allah subhanahu wa tala was promised to be preserved as well. Its something different than the modern Bible, both the Old Testament and the New Testament.