There are software engineers that specialise in source code analysis that lawyers will often use in these cases. The engineers will be given access to source code in secure environments where they're not allowed to bring any device in or out. They review, analyse, and write up a report using pen and paper, that can then be reviewed by the lawyers.

Absolutely. It was very similar to one of my first jobs: "Legal Technical Analyst". Not as much time doing deep source analysis, but basically translating things for lawyers: "So as far as this claim of copyright/plagiarism... this block here, that's CS 101 stuff, that block there, that's novel, and does x, y and z".