Connect app for Lemmy actually has this feature, and it really is a gamechanger. I mean, it makes Lemmy kinda into a desolate wasteland of posts, but its better than seeing most of the garbage I don’t care about and don’t want to interact with.

Granted, this also relies on users putting said keywords in the title of their post, so I still end up seeing stuff I don’t want to, but it is drastically decreased.

On browser you can put this onto your custom filters

lemmy.world##div.post-listing:has(span:has-text("/musk/i"))

Voyager has word filters : https://m.lemmy.world/