The texts it was translated from, the Masoretic Hebrew Old Testament and the Textus Receptus written in Koine Greek.

Again, there are some translation errors in the KJV, notably the use of the word unicorn to represent an extinct animal of some kind. Nobody is sure of the true meaning of the word, but modern translators have agreed to translate it as wild ox.

Numbers 23:22 (KJV)

God brought them out of Egypt; he hath as it were the strength of an unicorn.

Numbers 23:22 (NIV)

God brought them out of Egypt; they have the strength of a wild ox.

None of these errors affect anything of a doctrinal nature, while removing verses about the importance of repentance do.

The Vatican has fragments of the Alexandrian bibles, which were written in classical Greek, not Koine Greek, and carefully edited to remove evidence of Christ's divine nature. Codex Sinaiticus, another Alexandrian text, was found in a wastepaper basket in a Catholic convent on Mount Sinai by Tischendorf.

You can actually see how Codex Sinaiticus was edited in many places by viewing it on the official website- https://codexsinaiticus.org/en/

I know Wikipedia is a questionable source, but all of the above information can be verified there, including the fact the manuscript was edited in numerous places.

A paleographical study at the British Museum in 1938 found that the text had undergone several corrections. The first corrections were done by several scribes before the manuscript left the scriptorium.[62] Readings which they introduced are designated by the siglum אa.[79] Milne and Skeat have observed that the superscription to 1 Maccabees was made by scribe D, while the text was written by scribe A.[80] Scribe D corrects his own work and that of scribe A, but scribe A limits himself to correcting his own work.[8]

https://archive.md/tPHg8

Thankfully, it is due to persecution of the true believers that the real Bible was preserved throughout the Dark Ages, because the Orthodox Christians fled as far away as Russia to escape from both the Roman Catholic inquisition as well as Muslim invaders of Constantinople.

There was also the discovery of the Dead Sea scrolls in 1947 which verifies the Masoretic Hebrew and Textus Receptus (Koine Greek) are authentic. The Book of Enoch was also rediscovered at that time.

All of the Greek texts among the Dead Sea Scrolls are written in koine, the common dialect of the post-classical Hellenistic and Roman worlds and the New Testament language. A total of 27 Greek manuscripts have been identified from the Qumran caves.

https://www.deadseascrolls.org.il/learn-about-the-scrolls/languages-and-scripts?locale=en_US