Sounds like your partner could be struggling with a personality disorder such as Borderline or Narcissism, or possibly both, with histrionic traits. Keep in mind, an official diagnose can only be done by a licensed therapist. But you may want to look up videos on Borderline. Things may click for you.
What I did with my partner was export our whatsapp conversation to a text file, then threw that into chatgpt and asked it to look at the personality dynamics and possible disorders. It gave me a "diagnose" and I looked up videos and the puzzle pieces started to fall in place.
Both Borderline and Narcissism have their roots in childhood. If your partner is BPD for instance, it was caused by heavy trauma during the first years of childhood. This can be abandonment, abuse, etc. Not their fault. They are however responsible for their actions.
These people operate on a different system than others, and what's logical for you may not be logical for them. People with BPD have unstable moods and can act recklessly. They also have a hard time managing their emotions consistently.
In the case of my partner, it all of that is prevalent. My partner will also occasionally throw lies or accusations at me, just to cause chaos. Instead of defending yourself against those lies or accusations, try to look at the underlying issue. What is it that your partner needs? Reassurance? Validation? Safety?
That said. A large part of these relationships do not last if the mentally ill partner doesn't seek treatment. To add to the drama, they don't like to be told that they need treatment and telling them will result in more rage / manipulation.
If you must stay with your partnery, my advice would be to kindly but firmly assert your boundaries and protect them.