What I have sought to employ, rather than extensive attempts to prove any particular narrative, is to seek to apply one heresy in occasional conversations with cultists. If from time to time, such fanatic zealotry is confronted with a heretical fact, they are generally not immediately outraged and react angrily (such heresies aren't claims like 'The pope is diddling little boys' or smth that Catholics must immediately defend the pope from, but rather smth like '25% of the convictions for child abuse have been of Catholic Priests', which is non-specific enough to not trigger them to defend specific individuals, while also compelling them to themselves seek to disprove the true claim, which will cause them to search up supporting information that they cannot accuse me of lying about or making up).
While this can fail if I am too pointed, if I seek to simply counter a general principle or vaguely defined population of the cult, it can generally avoid being seen as a personal attack on their cult leader, but contrast factual reality with some cult precept essential to faith in the cult.
In this way I have had some success as enabling reason and factual information to penetrate the cults attempt to completely innoculate their fanatic adherence to cult indoctrination and propaganda by gently inserting proof of deception the cult - all cults, from religions to major political parties, essential indoctrination of sheeple, like the AGW climate alarmism corporation seek to impose in order to gain complete control of CO2, which is the basis for all life on Earth, so that they can eventually enslave humanity by controlling their access to air, water, energy, and food, ands similar deceptions for specific purposes, like the war on the Ukraine promulgated by war materiel contractors seeking to benefit from production of weapons by convincing people to support war, or donations of war materiel that can be fraudulently diverted by corrupt politicians or military brass and sold on the black market to cartels for covert cash, for example.
Overall, I just seek to introduce a fact, or even just the edge of a fact, that requires my interlocutor to themselves seek to disprove it, which cannot be done to actual facts.
Trying to convince cultists they're in a cult is not possible in a conversation. They can only gradually and incrementally be convinced to themselves accept facts that over time add up to proofs they have been deceived. Mark Twain has (falsely attributed to him, it turns out) said that 'It is easier to fool a man than to convince him he has been fooled.'
When people that are evolved to join and belong to societies that are essential to their success and felicity have joined some kind of cult that endangers them, they can only be gradually and gently enabled to themselves discover their cult is predatory, and not a beneficial society that they should be a member of for the actual benefits that improve their survival and felicity.