There is some evidence that inoculation and education can have a limited effect, both in terms of how effective it is and how long it lasts, on reducing the transmissibility of hate. It gives people protection and a pre-existing set of understandings that help give them resilience against hate content and the lies that underpin hate, but that doesn't change the fact that they are being bombarded.
We have something in our psychology called the illusory truth effect. If we see something frequently, we think it's more likely to be true. That's part of the reason that when we are being bombarded with hate content, we end up concluding there can be no smoke without fire, and we start to normalize hateful attitudes, conspiracy theories and lies.
The great replacement theory specifically is the theory that Jews are encouraging migration of Muslims and Blacks to destroy the white race through intermarriage and interbreeding.