https://lemmit.online/ is trying to archive Reddit, as are the people at r/DataHoarders (the link https://libreddit.projectsegfau.lt/r/DataHoarder/comments/146msr8/is_there_a_complete_backup_of_reddit/ will not give traffic to Reddit). https://the-eye.eu/redarcs/ is an existing Reddit backup, though I don’t know how complete it is.