These are some fine vintages of Elixir and OTP, both released ~3 years before Ubuntu 23.10.

I can’t offer any good solution of patching Ubuntu 23.10 for that, but what you could do is:

• Check out a more stable Linux repo. Debian might be a good fit as it has slower release cadence and longer maintenance period. OR
• Wrap both OTP and Elixir in a Docker container. Docker supports an official image with OTP 23, but alas not Elixir 1.11 (1.12 is the lowest on the website: Docker). Nothing prevents you from forking the OTP 23 image and installing Elixir 1.11 on it.

EDIT: The setup beam action on Github lists Ubuntu 20.04 as the one you’d need for OTP 23: GitHub - erlef/setup-beam: Set up your BEAM-based GitHub Actions workflow (Erlang, Elixir, Gleam, ...)