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There is an option in settings at least for me, 'show read posts' if you uncheck that they will disappear. It's not an easy access toggle though unfortunately.
Sadly, that also hides all your own posts, even from your profile page. Which is invonvenient if you also want to keep an eye on them.
This should be fixed in the next update
What are you using that has that option? I'm using liftoff but I don't think it can do that
You can do that in Voyager. It has a button for that.
Jerboa has that option.
That's just on lemmy.world website. But if I toggle that, it also changes what I see on Sync.
Sync also has a 'hide read' button although it unhides on page refresh - but it's handy for quickly finding fresh posts.