#jq recipe to select a (pseudo-)random non-reply post from your #Mastodon archive and display its URL and text:
jq '[.orderedItems.[]] | map(select(.type == "Create" and .object.inReplyTo == null)) | .[now % length] | .object | {url, content}' outbox.json
Could be fun going through your old memories. Might find something you want to repost!
Note that the “non-reply” part isn't especially reliable. Some replies have a null inReplyTo field. Not sure why.