It sucks.

I think even the most negative review have to have suggestions on how to improve. I think if they do plan on firing, they would have to show that you aren’t improving according to the plan they suggested. So they better suggest improvement plan, don't just criticize .

Of course they can also say you are laid off due to elimination of position or cutting funds. Then you can’t sue

I don’t know about law suit but I know people who win but many also lose. We have someone who was suing for wrongful termination for a long time and she lost. It could go both ways. It also might be pricey

I don’t know what you should do but I know what I would do. I’d look for other jobs and just leave asap. It would be too stressful for me. In my line of work unless someone is fired for a horrible offense, people are given an opportunity to resign or they’ll be fired. Everyone always resigns. It’s not fun but it’s better than being fired, I think. They better give some options

In the meanwhile I’d ask them for suggestions how to improve and play their game. It would buy you time to find a new job