Is there a way for SSGs to support viewer comments?

With something like Astro you can use React (or others, even vanilla) components that can either be fully server rendered, or sent to the client. With that you can allow people to post comments. As for how to render them, depends a bit on what you decide. You can either have comments displayed the next time the site is built, or you could have a posted comment trigger a build, or some other similar idea.

There's a good resource of available commenting systems for static sites here (not mine): https://darekkay.com/blog/static-site-comments/

Thanks for posting! I update that blog post regularly to keep up with all the possibilities. Ironically, I decided to remove the comments from my own blog a few years ago. Comments still reach me, though, mostly via email.

I’m a fan of Isso: https://isso-comments.de/