Unable to complete project

Senior SWE, 9 YOE. Recently joined a new company and team, was a cushy pay raise and a fully remote position. Within the first two months our engineering manager quit and left a very negative review of his time on the team. Following that I learned the turn over on this team is generally within the period of months, not years. There is very little documentation and only one woman has any tribal knowledge of the database with over 1000 interwoven and poorly optimized stored procedures defining the company’s business logic. All backend code is in prehistoric JS strung together with RPC calls. All DevOps is outsourced to India, and that goes about as well as expected. Despite this, the first five months went fine, delivered every task and project on time. Some of which were pretty intensive However, around month six I was given a very poorly scoped project. I did a technical write up based on the project managers description which was peer reviewed and approved. I received some aid from the veteran developer but many of our conversations left me with more questions than answers, or “just look in the code”. I don’t blame her as she’s stretched thinner than the rest of us. Been on this project for two weeks and it’s been a nightmare. Pulling sixty hour weeks trying to fit a square peg through a round hole. Never ran into a project I couldn’t complete before, but it seems as if I just don’t have enough system knowledge to handle this one correctly. Even our senior QA lead didn’t write an effective testing plan for the project. Feels like I’m beating a dead horse by voicing questions and concerns at this point. Tie in an on call schedule and mandatory company wide AI acceptance training and I’m feeling like I’m about to crack. Any of y’all been here before?