One of the interaction menu options (where "Cross-post / Send Message / Report Post / Block user / Block Community" live)
OR (preferably)
perhaps even one of the external buttons (next to Comment / Save / Original Post -OR- next to Upvote / Downvote)
should be the ability to either hide or collapse a given post so the things you've already seen take up less screen space
(but shouldn't be permanently lost to you so you can go back to something if you decide you want to look at it again)

Also, apologies if this is already suggested, I tried to search, and either it isn't there or the search function isn't very good.