The Ruby Orb is using RVM to install Ruby, but RVM requires a re-release whenever Ruby is updated. Ruby was updated to 3.1.0 on Dec 25, but RVM has not been updated, meaning the Circle Ruby Orb cannot be used with Ruby 3.1.0 that I can tell.
Although the aforementioned rvm release doesn’t explicitly mention support for ruby 3.1.0, I was able to successfully install ruby 3.1.0 via rvm using: