Who wrote the bible?

Hey all. I’ve recently fallen down a pretty deep rabbit hole regarding the writing of the Torah and wanted to know your opinions.

What is your opinion on the documentary hypothesis and supplementary hypothesis? If you do believe them, why? If not why? How can we be sure that certain lines are written by which sources when we don’t have copies of just the sources in their own? Why does different writing style signal different authorship? How can we be fully sure which line is which source when there are significant differences in the usage of the name of hashem between the Dead Sea scrolls, masoretic texts and Septuagint?

For those who believe in the traditional narrative, how do you explain the different uses of G-D’s name, certain passages contradicting each other, doublets like two creation stories, two Abram saying sarai is his sister to a certain king stories etc etc. most importantly, what makes you believe in the divinity of the Torah?

Videos supporting or debunking each position would be great thank you.

Open to everyone please I want to hear everyone’s opinion