There might be cases where you want to install and use Ruby with Anaconda or Miniconda. Normally, you would just use:

conda install ruby

By doing this, Ruby becomes usable. however, it will not compile gems that use native extensions. Since it is nearly impossible to use Ruby without utilizing native extensions, this method is not very practical.

Instead, you can simply install Ruby from conda-forge and install the compilers package at the same time:

conda install -c conda-forge ruby
conda install -c conda-forge compilers

This way, you can easily use Ruby within Conda environments like Anaconda or Miniconda.

If this does not work, check conda list to see if Ruby other than conda-forge may have been installed.

Enjoy your Ruby life!

Reference:
https://github.com/conda-forge/ruby-feedstock/issues/44