I'm trying to find out if it's better to quit or be fired if I'm facing what feels to be a hostile environment at work/

A quick summary - I had an undiagnosed medical issue that was accommodated by my employer for 3 years, and I had good performance reviews. My boss found out I had started to look for another job within the same company, and told me I couldn't leave and she couldn't bear to see me go because she trusted no one else in her department. A few weeks later, she got into trouble, and all of a sudden I was written up for poor performance, told that my accommodation would no longer be considered, and told that my job role changed. I was never given any explanation of how to improve my performance, no tangible measure of what constituted improvement, and no time frame for improvement. Any time I asked, I was denied an answer. HR removed me from reporting to my boss, but she continued to be involved in my day to day management. I have since gotten a diagnosis, but things are no better at work. My old boss is back to managing me, and HR told me to roll with the punches. I get yelled at daily.