I know very little but I do know its heavily tied with Mad Liberation. My therapist is a mad liberationist and the way she explains it is that if people's symptoms are distressing them n they dont want them, then she would like to help treat them. But if symptoms aren't causing distress, there is no need to make someone fit what's "normal."
This has meant things like accepting that I call myself insane and take pride in it rather than trying to become sane or convince myself that I am. She respects my decision to not medicate my schizophrenia, and helps me find patterns to predict it better and ways to cope when it's difficult.
When I had a psychotic break and split an alter who believes themself to be a Prophet of Filth, my therapist helped risk assess and on seeing that they were harmless and happy, she encouraged us to just allow them to believe it. She reassured us that if the sane don't have to prove their religion is real, neither do we, and that we as insane people deserve spirituality every bit as much as sane people.
Instead of pressuring us to quit all substances because we're an addict, she helps us analyse why we're relying on them so heavily, supports us when we do want to stop, but also supports us when we really don't want to stop. She helps with harm reduction, and always firmly believes we have a choice and autonomy.
So to us, Mad Pride is about respecting the autonomy of the insane, not trying to force them to become sane/normal, and loving them as they are because their experiences are beautiful, important, and part of what humanity is.