ruby-all-dev binary package in Ubuntu Focal armhf

 Ruby is the interpreted scripting language for quick and easy
 object-oriented programming. It has many features to process text
 files and to do system management tasks (as in perl). It is simple,
 straight-forward, and extensible.
 .
 This package depends on the respective development packages for every Ruby
 version currently supported by Debian. This will usually be a single version
 (the default one), but during transitions multiple versions might be
 supported.
 .
 To programmatically list all the supported versions, install the `gem2deb`
 package and run `dh_ruby --print-supported`. To determine which is the default
 version, just dereference the /usr/bin/ruby symbolic link.
 .
 If you are not building Ruby packages for Debian, you probably do not need
 this package.

Source package