I am answering here before this question gets closed.
I understand your position as I have seen and been through much in the academic sphere. Unfortunately there is a number of such cases in modern Academia where too often the main priorities have shifted away from bonafide scientific investigation and betterment of society.
My main advice is that you move on. As mentioned, you have changed your professional settings and found greater peace and enjoyment. There is nothing stopping others from doing the same as you did, so do not think you are entitled to rescue your ex-colleagues. A parasitic supervisor can only thrive where there is fair availability of dedicated minions.
Surely you feel like you ought to somehow stop this person. This is quite possible to be done. That depends on how much time/resources/reputation you would be willing to sacrifice. I strongly advise you to keep a safe distance and save your peace of mind. I list a number of relatively sane measures you can take which would help others in the place you just escaped and reduce this PI's power.
Science self-corrects from peer approval and high technical standards. That means the bad publications will eventually show. When negative exposure of publications happen in the short term, the responsible PI loses peer support and soon finds it harder to collaborate and publish more (rubbish). Surely the reputation of some "powerful" PI of today relies on a number of recently published papers, some of which in high impact (=highly visible) journals. Are these papers truly substantial, scientifically sound and useful? Take a careful read. In case there are glaring inconsistencies or obvious misconduct, do objectively expose those to others in the field. I recommend resorting to technical discussion websites such as Pubpeer.com, and contacting journal editors directly.
Give lectures to younger students and colleagues and describe objectively what befell you. Most victims of an abusive PI did not foresee those problems, nobody told them anything. Information is key to avoid being scammed.
Contact academic organisations empowered to defend students' rights. Warn them against this institution.
Find out from where this PI is recruiting victims and then better direct your lectures, contacts.
Consider writing a blog, even if anonymously. Perhaps even some Youtube channel with short explanatory/warning videos. Do not directly reveal the names of this PI or University. There is a lot of abuse going on in modern academia, and we need more victims talking about it. You may get a lot of attention and make a point.
I believe with trivial exposure you will weaken this person. However fixing the system relies on a lot more. Hopefully your divulged materials will help in that sense.
Good luck, and move on.