Difficult-Anything-1's journey

I recently started as an IT specialist at a large corporation and I'm currently in my probation period. I'm feeling quite frustrated with the onboarding process, which has been anything but smooth. From day one, my assigned trainer has been negative about the company and expressed doubts about my commitment, saying he wouldn't teach me everything like he did with the previous hire who left after two months. The training has been disorganized; I've mostly been sitting next to different team members or joining Teams meetings where I get bits of information about internal systems. There’s no structured training plan, and when I asked a lot of questions initially, I was told I was asking too many and needed to figure things out myself. I tried to adapt by researching on my own and asking fewer questions. However, during a meeting with my actual manager, I was told to ask for help whenever I needed it, which contradicted what my colleague had said. I’ve faced criticism for not knowing processes that I wasn’t taught, and sometimes asking a simple question turns into a quiz on terminology instead of a straightforward answer. To cope, I started creating my own manual to organize the fragmented information I was receiving. I shared it with my colleague, who promised to review it, but after a week of silence, I received an email with a new assignment to expand my notes into a comprehensive document that should be usable by someone outside my position. The catch? I have only five days to complete it, including a public holiday, while managing my regular support responsibilities. This situation feels like I joined a company without a proper onboarding process, and now my notes have turned into an assignment to create the knowledge base that the company lacks. I’m seriously considering using my probation period to leave, as I’m struggling with the expectation to independently reconstruct years of company knowledge while being judged on things I wasn’t properly taught. I’m curious if others in corporate IT have experienced similar onboarding issues and if this seems like a major red flag.