TL;DR

install dnf packages

su -
dnf install git

for ruby-build

dnf install autoconf gcc patch bzip2 openssl-devel libffi-devel readline zlib-devel gdbm ncurses-devel tar perl-FindBin

dnf config-manager --set-enabled crb
dnf install libyaml-devel

dnf config-manager --set-enabled powertools
dnf install libyaml-devel

git config --global http.https://github.com/.proxy http://server:port

cd /usr/local

git clone https://github.com/rbenv/rbenv.git rbenv
git clone https://github.com/rbenv/ruby-build.git rbenv/plugins/ruby-build

/etc/profile.d/rbenv.sh

export RBENV_ROOT="/usr/local/rbenv" 
export PATH="$RBENV_ROOT/bin:$PATH" 
eval "$(rbenv init - --no-rehash)"

exec -l $SHELL
rbenv -v

mkdir -p /usr/local/rust && cd /usr/local/rust/

export RUSTUP_HOME=/usr/local/rust
export CARGO_HOME=/usr/local/rust

export HTTP_PROXY=http://server:port
export HTTPS_PROXY=$HTTP_PROXY

no-proxy

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

with-proxy

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs -x http://server:proxy | sh

特に拘りがなければ1) Proceed with standard installation (default - just press enter)を選ぶ

/usr/local/bin/rustc

#!/bin/sh

RUSTUP_HOME=/usr/local/rust exec /usr/local/rust/bin/${0##*/} "$@"

実行権限を付ける

chmod 755 /usr/local/bin/rustc

他のrustc関連実行ファイルにもパスを通しておく

cd /usr/local/bin/
ln -s /usr/local/rust/bin/* ./

rustcだけは失敗するが、想定通り
ln: シンボリックリンク './rustc' の作成に失敗しました: ファイルが存在します

exec -l $SHELL
rustc -V

rbenv install -l

ここで出てくるものから選ぶのがおすすめ

rbenv install 3.4.1

rbenv versions
rbenv global 3.4.1

ruby -v