I deal with these issues the same way I deal with all relationship issues - open communication, assertiveness about my perspective and understanding about my partner’s.
I expect my fiancé to deal with these issues the same exact way, as he (almost) always has. The most vital part of someone’s character is how they respond to new information or feedback - NOT what they knew coming in. Anyone can say ignorant things, but if they defend it like their life depends on it, there’s real trouble.
My fiance had an ex FWB. One day I overheard him on call with his friends while we were both home, calling this ex FWB all sorts of sexist names. I confronted him about it after. I knew the story - he was just as much to blame as she was but somehow he "lost all respect for her" because of her relationship to him specifically (aka sexual)…
He explained that he used those words about a woman he doesn’t respect, not because he doesn’t respect women. I counter with the fact that he judged a woman’s entire worth five years later, solely due to their personal relationship that he took just as much of a part in. Back and forth and back and forth, then we come to "I just didn’t think about it like that, you’re right."
Sigh… But I forgive him, because he’s always open to having his opinions challenged and when he sees where I’m coming from, he never makes the same mistake twice. And because we have such long, detailed and open conversations, I know exactly where this stuff comes from. So I can trust that he’s not sexist, he’s just not used to second guessing the casual insults that his friends use in private (and as an introvert, he’s not exactly itching to renovate his 5 friends lol).
If he were the sort that dodges every question, acts shady and says "I don’t care" to any convo beyond surface level, we wouldn’t have lasted. I couldn’t stand a partner like that, especially when it comes to the important conversations.