Due to the decentralized nature, and multiple communities on same subject exist across multiple instances, it is not uncommon for people to be subscribed to multiple communities of the same subject. It is also not uncommon for people to submit the same thing to multiple communities of the same subject, thereby resulting in multiple posts of the same content appearing in the feed. Cross post or not, the duplicated content clutter the feed, making it more difficult to consume content quickly.
I think it would be helpful to declutter by hiding/collapsing these posts. A possible implementation could be to keep an index of post titles, author, and submission time; then hide/collapse (cross)posts with same title, submitted by the same author, within some time interval (say for example +/- 1hr). That way the feed wouldn’t be as cluttered.
I understand cross referencing each post against other known posts is an exponentially large task, and could be very resources consuming, so even with the time range filter, it would be prudent to make this an option and likely disable by default to prevent performance issues.
It may be nice to inform the user on the post itself that there are other similar discussions, if they’re interested for other comments/interactions, but that’d be a nice to have in the future kind of thing.