Failed probation for struggling with my mental health - Senior Research Executive Verian Group Employee Review

I worked at verian for 6 months and had an incredibly negative experience. It started when I got told off by a manager for sharing reflections from an external meeting and asking questions about a task in the first month of my employment. Due to this and some external factors I started struggling with my mental health. When I shared this with my line manager her solution was to extend my probation to "make sure I was a good fit for the company". Shortly after this I had an incredibly tiring week where I was once again told off for taking toil which had been prearranged following a 14 hour work day and for taking care to perform the tasks I was assigned in a safe way. This led to a serious decline in my mental health. My goals for my probation quickly changed from competency based to mental health based including things such as improving my attitude and not getting defensive at criticism (both symptoms of my deteriorating mental health). I managed to somehow pull myself out of the hole I fell into 3 weeks before my new probation end date and started meeting all of the goals that had been set. I had a meeting with my line manager who expressed that I was passing my probation despite the company not being impressed with my work and having a lot of places to work on. No mention of any good work I had done is expressed and the improvement in my mental health and work is not mentioned in this meeting at all despite being highlighted previously. I write to my line manager afterwards expressing that the meeting felt very negative and I need feedback to be constructive in order for it to be helpful and ask her to please try to be constructive in the future. She calls another meeting where she explains that I'm not allowed to feel this way and that she has to be honest and give honest feedback to me. This sends me back into a very very dark place and I realise that I need to change line manager as I can not continue working with her if that is her attitude to constructive feedback that I had given her. I wrote to HR and explain the situation and ask for a new manager that I has already asked and agreed with. Instead HR calls me into a meeting and tells me that I am going to be put on a month of mental health leave. When I express that this may not be useful for me as I need routine to maintain my mental health they explain that this isn't for me but rather to protect the team in case I were to do anything to myself. The first day of my mental health leave I get an email explaining that they will wait until the end of my mental health leave to make a final decision on my probation (which I obviously ignore). 1 week before my mental health leave is set to end I get an email explaining that we needed to have a discussion about the result of my probation. At the meeting I get told that they are deciding to fail my probation. When I ask why they say that they don't think it's useful to go over this again as I already know. As I was told that I would pass and then after less than a week of working was put on mental health leave and then failed I have to assume it is because of my mental health. I explained this and how most of the goals I were given were heavily related to my mental health to HR and was told that the company was not able to accommodate people who were not able to take criticism. Other cons included: - no interest in improving practice (I got told not to use the term best practice as it made people feel like I thought they weren't doing what was best) - many employees have worked there for most of their career and believe that their work is perfect and cannot be improved - diversity is a serious issue