Users can now block instances. Similar to community blocks, it means that any posts from communities which are hosted on that instance are hidden. However the block doesn’t affect users from the blocked instance, their posts and comments can still be seen normally in other communities.
If they used the native instance blocking feature to “completely block” the instance that actually only hides posts from that instance.
From https://join-lemmy.org/news/2023-12-15_-_Lemmy_Release_v0.19.0_-_Instance_blocking,_Scaled_sort,_and_Federation_Queue