Do you have an example of your work? I'm curious what a report looks like, having done only a couple of 'code reviews' myself (that is, I got a codebase and three days to write a report on how it could be improved, not very formal at all).
I've been a part of a few of these, and it really just depends. Overall, though, the report will break down the company into a bunch of different categories (and not just from a code/tech stack standpoint). Sometimes you'll get a point-rating (1-10 or whatever) or a market-based rating (e.g. degrees worse, comparable or better than their competition in a category).
The audit may encompass anything from code quality, technical debt, tech stack, architecture, infrastructure, to the product roadmap, licensing of dependencies, corporate structure, hiring/retention of talent, etc. It really just depends on what the company paying for the DD asks for (which could be either side, and that also matters a lot).
Each category in the final report will have a summary, a score, notes about risks/opportunities, suggestions on how to improve, what things are strengths, etc. It can be really, really long, and often it's broken up and worked on by multiple people based on their area(s) of expertise. Usually you'll see a high-level summary chart at the end of the report that just kind of puts everything in front of you.
Do you know of any documents similar to what you do that have been disclosed to the public, or is this a sub-industry that us completely opaque to outsiders?