CSS:

    pre { whitespace: pre-wrap; }

https://www.w3schools.com/cssref/pr_text_white-space.asp

That's what I've included in my own HN Stylus stylesheet for years. Works on Desktop or Firefox/Android, but other mobile browsers don't support it, for lack of extension support.

Updating the HN markup to offer true blockquote support would be a more complete, though less trivial, solution.

I've suggested the first myself repeatedly.

pg asked how to fix this, and was given the solution, on HN, nine years ago:

https://news.ycombinator.com/item?id=592603

The suggestion's been made numerous times:

https://hn.algolia.com/?query=whitespace%20pre-wrap&sort=byP...

Make groups of `/^\s+> /` lines turn into a `<blockquote>`. Render it slightly indented and italicized.

I don't think the major problem is that `/^ {4}/` lines don't wrap in a way that's useful for quotes; it's that there's no way to format quotes so people use the only formatting element HN has.

Markdown renderer?