Smaller user base and a lot of community overlap makes the same things appear quite a bit.
Lemmy Support
Support / questions about Lemmy.
Maybe basically switch sorting from "top" to "new"
That's what I did.
Go into your settings and unclick show read posts , and save. Then you won't see any of the same posts again after you've read them.
Sort by New Comments, or by Scaled sort (which boosts under-active comms).
I have my client (Summit) set up to mark posts as read when I scroll by and to hide them. It can alao mark crossposts as read. Then I just browse by Scaled. Occasionally I switch to Top over x timeframe when I have been away for a while.
I like to sort by Subscribed+Scaled, or sometimes Subscribed+"New Comments" (forums style)
also maybe subscribe to more communities https://lemmyverse.net/communities
in the settings there's an option to "Show Read Posts", you might want to uncheck that so you don't see the same posts again
but also... stop checking so often! lol
I go by all but I block communities I have just zero instance in. I select the setting to not show things in my feed that I have read or interacted with. Works for me.
No Fediverse platform I know of uses algorithms like the ones in today's mainstream social media, so you'll have to get used to seeing the same thing every hour or so. Try subscribing to even more communities, changing sorting algorithms or browsing the "All" feed.
I occassionally find and remove communities through the "All" feed or random "recommend me communities" posts in communities such as:
Try creating a post in one of them.
If you want to help build a new community, try finding new ones. Creators of new comms usually post them in comms such as:
I do wish that there was a "Random + New/Scaled/Hot" sort.
if you want to browse All, I would suggest not being shy about blocking communities