depends on what you want, the low end is incoming comments as emails and putting them semi-manually into an iframe on the unchanged static article page. Doing it myself at https://blog.mro.name/2019/05/wp-to-hugo-making-of/ and sacrificed commenter speed.
Others may easily be more sophisticated than above brutalist solution. But still: comments in iframes align well with static sites IMO.
Edit: even better may be to phase in comments from HN or the fediverse or whatever you care about into an iframe. Be it copied or inline and re-styled.
Today that’s cloudflare but in the past it was varnish.
Otherwise it is very dynamic. Different users have access to different content so we generally can’t cache full pages at the edge for authenticated users.
not yet, but I think of a delayed shell script (cron 15min?). JS (clientside) may be not of much use.
Or use a feedback webform via https://github.com/mro/form2xhtml - doesn't have to be email then.
Or monitor IMAP folders for accepted comments and cron them to the webserver a la https://codeberg.org/mro/flohmarkt.monte-ts.de/src/branch/ma... and online.sh
But that's not actually solving the problem, it's just offloading it. Not to mention that you're selling your community to yet another tracking company, and jacking up user page load time.