My mother constantly humiliates me and points out all my bad sides, not seeing the good ... What to do?

Do you live in the same territory? Are you financially dependent on it? If yes, then separate as much as possible (if you are not a teenager), if not, then reduce communication to such quantity and quality when you will not feel discomfort.

Try to go to family therapy, having previously agreed with your mother. This is a good working option.

nah *** send.

no, seriously, what else can you do here?))

you finish the things that are needed for a person - and get out.

and let the person criticize the teddy bear.

I had a similar situation with my father, the acute perception of his criticism simply subsided over time (in late adolescence, specifically), the ability to emotionally abstract and fend off appeared. You, apparently, do not have such an ability yet.
I do not know your mother personally, and therefore I cannot say how constructively it is possible to conduct a dialogue with her, whether there is an opportunity to explain something, to shake her point of view. Let's say no. Then you just accept it, realizing that there is a significant dissonance between mom's words and objective reality. Emotionally, it makes no sense to succumb to her provocation in the form of humiliation - perhaps it was started precisely for this purpose (to throw you off balance).