To fair, I think the only way to executevthat would be to implement an image recognition algorithm, as I don’t see lemmings marking arachnids as a tag on their posts even as arachnophobia is one of the most common phobias out there (to be fair, I think Mastodon has stronger culture for tagging trigger warnings).
That said, if you have SLIGHT arachnophobia, I’d almost recommed exposure thereaphy with a professional psychiatrist, as if you have some tolerance, it’s easier to work on than full on panic without ant tolerance.
I tought hiding read posts was a feature of Lemmy itself. To be fair, I swapped to Connect from Jerboa after I suggested quality of life update UI, and tge response was rather hostile in my opinion. I mention that because in Connect, hiding posts and comments is bit too easy, as I tend to do that mostly by missclicks.
That said, I’d imagine implementing a feature to hide post shouldn’t be too hard of a task to program in, I’d imagine.