Sync for Lemmy

You can change it so that it marks all scrolled posts as read here: Settings shortcut: History > Mark posts as read on scroll

If you enable the FAB, you can arrange your frequent actions so that "hide all read posts" is first. Then, when you long press the FAB, it will hide all read posts. Settings shortcut: General > Show FAB

FAB action has to be set to "more actions" (or whatever it's called). Alternatively, you can just set the action to "hide read", but that will remove your ability to use the FAB for other actions.

My hidden read posts in Sync comes back, when I refresh. Maybe a bug -_-

Voyager lets you mark a post as read if you upvote or downvote it as well. Would love for that feature to make it to Sync at some point.

Only app I've noticed that has this is Voyager, very useful feature

Please correct me if I'm wrong, I'd like to know what other apps support it

If you hit the three dots at the top right a menu appears and there's an option for hide read posts. I haven't tried it yet though to see how it works.