As described in the referenced spec, the underscore is a perfectly valid and widely used character in CSS identifiers. drupal_clean_css_identifier should not transliterate underscores by default! Even the comments in the code say that the underscore is a valid character.
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
You're right @mlncn, a single underscore is changed into a dash in Views classes in Drupal 11, and I just updated an issue about this. It looks like it's intentional, and not a bug, so documentation is perhaps the solution?