To try to red pill a hard core leftist IRL via another persons, like yourself, influence have something like a 99,9% failure rate. Afaik the most succesful way to get anyone to leave such a cult, is to bait them with a subtle step into research everything by themselves so that a person stuck in this mindset should feel like they have their own moment of epiphany. However when they are showing signs of leaving the cult, you should support it 100% without overdo it.

The walkaway testimonies have a lot of good examples.