TL;DR

requirement

dnf install --enablerepo=powertools libyaml-devel
dnf install git

RHEL 9系では別のリポジトリらしい

git clone https://github.com/rbenv/rbenv.git ~/.rbenv

echo 'eval "$(~/.rbenv/bin/rbenv init - bash)"' >> ~/.bashrc
exec -l $SHELL

rbenv -v
rbenv 1.3.0-4-gc335ab8

git clone https://github.com/rbenv/ruby-build.git "$(rbenv root)"/plugins/ruby-build

rbenv install -l
3.1.6
3.2.5
3.3.5
jruby-9.4.8.0
mruby-3.3.0
picoruby-3.0.0
truffleruby-24.1.0
truffleruby+graalvm-24.1.0

rbenv install 3.3.5

rbenv versions
# 3.3.5

rbenv global 3.3.5

ruby -v
# ruby 3.3.5 (2024-09-03 revision ef084cc8f4) [x86_64-linux]