A buddy found Cusdis - a self-hostable Disqus alternative: https://cusdis.com . But this only does comments, no pingbacks - and via a separate product that you need to integrate using JavaScript.

And running this opens you up to security issues you were trying to avoid by going the SSG route. In a way you could just keep WP, then.

(Also, WP has this beautiful ActivityPub plugin that makes your blog a fediverse account that people can subscribe to and even comment on your posts from Mastodon/Pleroma/etc.)