Because I have basically nothing in my feed on this account, Facebook backfills it with "recommended" posts and I was pretty shocked at how universally terrible they are. [...] since I've provided very little in the way of alternative information or interaction for it to use
There is your problem.
When an information-hungry platform like Google or Meta asks you to fill out your preferences "to serve you more relevant content"... they are not lying. I mean, it's also to select ads that will pay more for your attention, but the thing with the content algorithm is, if you don't give it data, then it will ass-u-me that you're statistically most likely to engage with content that is getting most engaged... by people who have also not provided it any data.
The problem with that cohort, is it not only includes the few people with legitimate security concerns, but also those who got dark secrets to hide, and/or are using "incognito" browser mode to look for porn.
I don't like to give too much info about myself, but I also don't want to get stuff intended for the "average horny fanatics" group, so I try to give enough data for the algorithm to put me into a group that makes more sense to me.
And it works. The strongest signal you can send to the algorithm, is blocking content you don't want to see. It's amazing how quickly modern algorithms learn to avoid showing me most porn, politics, or religious content, and instead show me science and humor. They still send like 1% of trash my way, clearly checking whether I'll maybe engage with it, but report+block works wonders.