What could be the outcome of writing negative things about previous university in an application to another university?

Applications are places to write positive things, not negative ones.

Negative circumstances can paint you in a good light if you can describe how you have overcome those obstacles. Stated as you have here, the descriptions of your previous environment sounds more like blame, especially this part:

They are not at all helpful or encouraging. They always need to boost their ego, never ready to discuss anything, never ready to accept their mistakes if they made one. The teacher-student relationship is more like, dare I say, a master and slave type of relationship.

Maybe the blame is valid, however, when you talk negatively about someone else, people will reflexively wonder whether your complaints are justified, and they may worry you will describe them the same way. If you say your institution only drove you to memorization, how does this demonstrate you've developed skills related to research?

That said, mental health is very important, not for PhD applications but for you. I strongly suggest you seek professional assistance with those concerns - this is much more important than any PhD application.

If you must comment on how your previous academic experiences were "difficult", then try to couch them in language that is not assigning blame. An approach to try is to document what skills and lessons you did learn, and how those hardships (?) informed your growth, as a person and a prospective academic. These attributes are not reflected in grades, and this is the section to explain what you will be able to contribute to this new institution.

The main reason to not speak ill of your previous supervisors is because people at different institutions talk to each other. If you express how your previous supervisors were a bad fit for you, chances are those on the selection committee will contact the previous institution to get "their side". Since the word of a colleague carries more weight than a student, that would not be in your best interests.

Lastly -- and most importantly -- if you are having suicidal thoughts, please please please reach out. I am sorry that I don't know how to frame my advice in a compelling way, but I do know where your head is at. Academia can be very unkind. Just remember that support is always available.