Apologies if this is the wrong place (perhaps I should open an issue in ruby/ruby for the NEWS.md instead?).

We've found an undocumented breaking change in Regexp.new that was put in place for https://bugs.ruby-lang.org/issues/18797

ruby/ruby@7e8fa06 changed the interface to issue a deprecation warning for the third parameter (in Ruby 3.2.0) and ruby/ruby@04cfb26 actually removed it (for Ruby 3.3.0)