My 35M fiancée 38F is upset with past social media posts

My (35M) fiancée (38F) and I have been together for 4 years now, and every once in a while, she’ll go through my public (to friends) Facebook friends list, go through posts and/or photos and see if I’ve commented on things, though only of other women’s pages. I barely use social media these days, so anything she finds is from the distant past, often years before her and I met. She’s found posts (anywhere from 1-15 years prior to us meeting) where I’ve called my platonic female friends beautiful, or posts where my friend or I will say something like “can’t wait to hang out” or she will find a photo that I liked or hearted. This results in her assuming that there was some attraction or “something there between you two” because she claims friends just aren’t supposed to talk to each other that way if they are of opposite sex. She’s bi and calls other women beautiful and hearts their photos, for context. When shes found something new and brings this up to me, I’ll reassure her that I’m not interested in them, and that regardless of what old Facebook posts say or what I’ve said in the past before we met, that I’m with you now and you’re what matters to me. This never seems to be good enough and I’m often accused of lying, a this often results in a heated argument. Because she can see that I’ve used the word “beautiful” with someone else in the distant past that that word somehow means less if I call her beautiful. She’ll often demand that I unfriend these friends who she’s found that I’ve conversed with on Facebook, regardless of any of my explanations.

She also knows that when she goes through old social media posts that she’ll get triggered and she’ll do it anyways. I’ve stopped using social media for a few reasons, but one of them being I’m concerned that it’s going to cause her more stress as well since she’ll likely misconstrue something between a female friend and I. I’m not a fan of her using social media because I see what sort of anguish this causes her, but I also wouldn’t demand she stop using it because that just seems like the wrong way to approach anything (with demands)

What can I do or say to help her understand that this is just how I used to be on social media, and that has no bearing on me or us now? I’d also love any advice on how to frame how people can have plutonic friendships between men and women because any of my explanations get quickly dismissed as me just “trying to keep these females around because there must be something there”

TLDR: my fiancée goes through my Facebook friends and gets angry at me for posts before we met and thinks I’m secretly interested in all of my female friends