Install instructions fail at "Installing Ruby" on Debian 13 (Trixie)

When trying to install on a new Debian 13 (Trixie) VM following the official installation instructions at https://docs.joinmastodon.org/admin/install/ it fails at section "Installing Ruby". **Instruction** `RUBY_CONFIGURE_OPTS=--with-jemalloc rbenv install` **Result** ``mastodon@server:~$ RUBY_CONFIGURE_OPTS=--with-jemalloc rbenv install rbenv: no such command `install'`` I do not use Ruby on any other project I work with so have no place to start solving this problem.