The current runner (ubuntu-22.04-arm64) was detected as self-hosted because the self-hosted input was set. In such a case, you should install Ruby in the $RUNNER_TOOL_CACHE yourself, for example using https://github.com/rbenv/ruby-build You can take inspiration from this workflow for more details: https://github.com/ruby/ruby-builder/blob/master/.github/workflows/build.yml $ ruby-build 3.2.3 /home/runner/work/_tool/Ruby/3.2.3/arm64 Once that completes successfully, mark it as complete with: $ touch /home/runner/work/_tool/Ruby/3.2.3/arm64.complete It is your responsibility to ensure installing Ruby like that is not done in parallel.