Thing is, a cross post is nothing special. It’s a) a post with an identical link, and b) a post with “cross posted from…” appended to the body content.
It is still just a post. Lemmy (and k/mbin) just attempt to mask the fact there are multiple of them.
I don’t know if it can be done any better though, ActivityPub has quite a few quirks.
Hugo can be as simple as installing it, configuring a site with some yaml that points at a really available theme and writing your markdown content.
It gets admittedly more complex if you’re wanting to write your own theme though.
But I think this realistically applies to most all static site generators.