Jekyll, technically, works with Ruby 2.4.0. However, some of its dependencies may require a newer version of Ruby. At the point of creating this memo, the 2.7.0 is the freshest version. Jekyll and its dependencies work with it fine.
When installing Ruby via brew, the freshest version will be installed by default. It is still required to add the path
to the binary dist in the $PATH, for example:
/usr/local/Cellar/ruby/2.7.0/bin/
In many cases, gems are provided with C-lang native extensions. The extensions are not compiled for all the combinations
of operating systems, operating system versions, and Ruby versions. If a pre-compiled extension artifact is missing,
gem will attempt to compile it locally.
On MacOS of versions 10.14 and 10.15, the compilation may fail with a number of errors pointing at the resource.h
C-lang file. In this case, follow this answer on StackOverflow: rename
the /usr/local/include directory to something else, e.g. /usr/local/include_old, so that the C compiler goes not
look there for the System API by default.