People are working on this. In particular Retro Guy has one very good web front end that is really the only viable replacement for Google Groups at this point. Look for Rocksolid Light (rslight) on gitlab.

The source code is here: https://gitlab.com/rslight-public/rocksolid-light

The live demo site is here: https://news.novabbs.org/rocksolid/index.php

It has a retro look on purpose. There are several themes included and it is really easy to create a new theme CSS file.

You can run a peer to carry text groups on a raspberry pi or a cheap VPS. Visit the rocksolid.* hierarchy on Usenet if you have questions about running a peer. Please don't ask questions about Rocksolid here on HN, as that would not benefit the people learning in the newsgroups.

Disclosure: I am not the maintainer of Rocksolid Light and I am not promoting my own product. I just like the software and I think the maintainer has the right ideas and right attitude of retro-styled usability in his project.